Lectin domains in the toxin of Bordetella pertussis: selectin mimicry linked to microbial pathogenesis

The pathogenesis of many infectious diseases is critically determined by prokaryotic lectins which enable differential recognition and activation of targeted eukaryotic cells. Some bacterial adhesins mimic and co-opt eukaryotic cell-cell adhesion motifs. This is illustrated by the toxin of Bordetella pertussis. Pertussis toxin mediates intoxication of eukaryotic cells by elevation of cAMP and it serves as an adhesin binding the bacteria to ciliated cells and respiratory macrophages. These activities are mediated by the lectin-like properties of the binding oligomer of the toxin. A comparison of pertussis toxin and the selectins involved in leukocyte trafficking indicates that these prokaryotic and eukaryotic C-type lectins share some element of primary sequence similarity, three dimensional structure, and biological activities. Such mimicry suggests a link between eukaryotic cell-cell adhesion motifs and microbial pathogenesis.

Patterns of p53 mutations in squamous cell carcinoma of the lung. Acquisition at a relatively early age

Squamous cell carcinoma (SQCC) of the lung is thought to arise after the accumulation of multiple mutations, including p53. To better characterize when p53 mutations are acquired, 37 SQCC of the lung were examined by polymerase chain reaction and single-strand conformation polymorphism analysis. Somatic p53 mutations were detected in nine tumors (24.3%). There were no significant differences in the stage, sex, or race between patients with or without p53 mutations. However, the patients with SQCC and p53 mutations were significantly (P = 0.0006) younger (mean age, 54.3 years) compared with patients without p53 mutations (mean age, 65). The topographical tissue distributions of the p53 mutations were examined by selective ultraviolet radiation fractionation. In all nine cases, the specific p53 mutant alleles were homogeneously present throughout the primary tumors, in all three examples with in situ carcinoma, and in all four cases with metastases. In one case, squamous metaplasia contiguous with the primary tumor also contained the same p53 mutation. Normal or hyperplastic and metaplastic or dysplastic epithelium not contiguous with the primary tumors lacked the specific p53 mutations. These findings suggest that p53 mutations are commonly acquired at a relatively early age, before the bulk of clonal expansion, and usually persist throughout the progression of SQCC of the lung.

Evaluation of growth, cell proliferation, and cell death in bovine corpora lutea throughout the estrous cycle

To evaluate the kinetics of luteal growth, bovine CL were obtained from four stages (stage I, Days 1-4; stage II, Days 5-10; stage III, Days 11-17; stage IV, Days 18-21) of the estrous cycle, and luteal fresh weight as well as DNA, protein, and progesterone contents was determined. To evaluate the relative rate of cell proliferation, proliferating cell nuclear antigen (PCNA; a specific marker for cell proliferation) was immunolocalized in paraffin-embedded luteal tissue sections. To evaluate the relative rate of cell death, nucleosomal fragmentation of DNA (a specific marker for apoptosis) was detected by agarose gel electrophoresis and also by histochemical localization in paraffin-embedded luteal tissue sections. Luteal fresh weight and DNA, protein, and progesterone contents increased (p < 0.01) from stage I to stage II, were similar between stages II and III, and then decreased (p < 0.01) from stage III to stage IV. The ratio of protein to DNA (an index of average cell size) was similar for stages I, II, and III and then decreased (p < 0.01) at stage IV. For stage I (corpora hemorrhagica), most proliferating (PCNA-positive) cells were located in or around the core of the tissue infoldings (presumably thecal-derived areas), whereas relatively few proliferating cells were located at the periphery of the tissue infoldings (presumably granulosa-derived areas). For stages II, III, and IV, the majority of proliferating cells appeared to be small cells (i.e., small parenchymal cells, fibroblasts, and endothelial cells). The labeling index (LI; percentage of cells that were PCNA-positive) was greatest at stage I (20.3 +/- 1.1%); it then decreased (p < 0.01) by stage II and was similar at stages II, III, and IV (3.4 +/- 1.1%). Apoptosis, as determined by evaluation of nucleosomal DNA fragmentation by agarose gel electrophoresis and in situ localization, was detectable only at stage IV. These data demonstrate that luteal growth from stage I to stage II resulted from cell proliferation as shown by a high LI at stage I, accompanied by increased luteal DNA content but no change in average cell size, and by similar protein: DNA ratios. Luteal regression from stage III to stage IV was primarily associated with cell deletion and decreased cell size as shown by a decrease in luteal DNA content and the appearance of apoptosis along with a decrease in the luteal protein: DNA ratio.(ABSTRACT TRUNCATED AT 400 WORDS)

Neuropeptide Y inhibition of nicotinic receptor-mediated chromaffin cell secretion

Neuropeptide Y (NPY), a widely distributed peptide with varied activities, inhibits nicotinic receptor-induced [3H]norepinephrine ([3H]NE) secretion from bovine chromaffin cells. The secretion produced by membrane depolarization with high KCl concentrations or veratridine is not inhibited. Fragments of NPY, such as NPY18-36, are potent inhibitors of [3H]NE secretion, whereas [Leu31,Pro34]-NPY and peptide YY have no effect. The response to NPY18-36 is not sensitive to pertussis toxin pretreatment of chromaffin cells. NPY fragments also inhibit nicotinic receptor-induced 45Ca++ influx but not that induced by KCl or veratridine. The rank orders of potency for inhibition of [3H]NE secretion and 45Ca++ influx are the same: NPY18-36 > or = NPY26-36 > NPY13-36. NPY and NPYfree acid are weak inhibitors of secretion but not 45Ca++ influx. Moreover, the IC50s for NPY18-36 inhibition of [3H]NE secretion and 45Ca++ influx are comparable, 1.4 x 10(-6) M and 0.9 x 10(-6) M, respectively. Regression analysis produced a correlation coefficient of 0.9842 (P < .0001). It was concluded that NPY inhibits [3H]NE secretion by a modification of the nicotinic receptor-mediated increase in Ca++ influx. The characterization of the response suggests that the NPY effect is mediated by a previously undefined NPY receptor subtype that was designated Y4.

Cell growth on immobilized cell-growth factor. 10. Insulin and polyallylamine co-immobilized materials

Polyallylamine, which is cationic and enhances cell adhesion electrostatically (non-specifically), was co-immobilized with a cell growth factor, insulin, onto a surface-hydrolysed poly(methyl methacrylate) membrane. The adhesion of mouse STO fibroblast cells was accelerated by the immobilization of polyallylamine. The adhesion and growth of the cells were both markedly accelerated by the co-immobilization of the polyallylamine and insulin. The co-immobilized membrane can be applied for a new technique for protein-free cell culture.

p53 mutations and microsatellite instability in sporadic gastric cancer: when guardians fail

Genetic instability may underlie the etiology of multistep gastric carcinogenesis. The altered microsatellites observed in tumors with the ubiquitous somatic mutation (USM) phenotype may represent the expression of such instability. Similarly, p53 mutations may allow the accumulation of genetic alterations caused by multiple mechanisms. In 40 sporadic gastric adenocarcinomas, nine tumors (22.5%) with p53 mutations in exons 5-8, and six tumors (15%) with the USM+ phenotype, were detected. None of the tumors had both alterations. The tumors with p53 mutations were predominantly in the proximal stomach whereas the USM+ tumors were predominantly in the distal stomach. The mutant p53 alleles were homogeneously distributed throughout the primary tumors, but usually absent from adjacent normal or dysplastic epithelium, indicating that p53 mutations are typically acquired before the bulk of clonal expansion. The loss of mutant p53 alleles during progression was also rarely observed in metastatic foci. Altered microsatellites were homogeneously present in the USM+ primary and metastatic tumors and one synchronous tubular adenoma, but were not detected in adjacent normal and metaplastic epithelium. These findings also demonstrate that the USM+ phenotype is expressed before the bulk of clonal expansion. In most (5 of 6) USM+ tumors, the sizes of the altered microsatellites differed between regions, indicating that the instability usually persists during clonal expansion. These findings indicate that both p53 mutations and the USM+ phenotype are present prior to the bulk of tumor growth and therefore may contribute to, rather than be a late consequence of, malignant transformation.

[Effects of retinoic acid on the adhesion and motility of metastatic human lung cancer cell subline (PGCL3)]

Effects of all-trans Retinoic Acid (RA) on the adhesion and motility of metastatic human lung cancer cell subline (PGCL3) were observed in vitro. The results showed that treatment of PGCL3 with RA for 5 days decreased the adhesion of cells to laminin substrate and the migrative ability through the polycarbonate filter of Boyden chamber, and those inhibitory effects became more obvious with the increase of RA concentration. Further investigation by DNA-RNA dot blot hybridization and immunohistochemistry denoted that RA-treated PGCL3 cells expressed lower level of 67-KD LN-R compared to untreated cells. The data from DNA-RNA dot blot hybridization also showed that RA could reduce the expression of AMF-R significantly. These results raise the possibility that the previously reported suppression by RA of PGCL3 invasion and metastasis may be related to suppression of cell adhesion and motility resulting from the decreased expression of the LN-R and AMF-R respectively.

Altered growth behavior of human cervical epithelial cells transfected by HPV type 16 and 18 DNA

Transfection of primary human cervical epithelial (HCE) cells with full-length HPV type 16 and 18 DNAs resulted in cell lines that could grow continuously. Four HPV DNA-immortalized cell lines were established. Morphologically the immortalized cells resembled primary HCE cells. Electron microscopy showed that they contained desmosomes and keratin filaments, which are characteristic structural components of epithelial cells. Each cell line had a unique integration pattern of HPV DNA but the transcription patterns were similar in the 3 HPV 16 DNA-immortalized cell lines. The expression patterns of viral DNA in the HPV 18 DNA-immortalized cell line were similar to that in HeLa cells, suggesting transcription of mainly early viral genes. The cell lines, unlike HeLa and SiHa carcinoma cells, did not form tumors in nude mice or grow in soft agarose, but collagen raft culture indicated that the immortalized cell lines had lost the capacity of normal differentiation compared with primary HCE cells. Morphologically, the aberrant differentiation of the immortalized cells showed great resemblance to cervical intra-epithelial neoplasia. The altered pattern of growth and differentiation of human cervical epithelial cells transfected by HPV 16 and 18 DNAs is in agreement with the view that HPV types 16 and 18 play an important role at an initial step of human cervical epithelial carcinogenesis but that co-carcinogenic factors are necessary for full malignant transformation in vivo.

A densovirus newly isolated from the smoky-brown cockroach Periplaneta fuliginosa

We purified a causing agent of fetal disease for smoky-brown cockroach Periplaneta fuliginosa, which was designated as "cockroach small spherical virus (CSSV)". Purified virus particles had a diameter of 22 +/- 0.6 nm and contained DNA as a single-stranded form. However, the extraction of DNA under condition of appropriate high salt and elevated temperature yielded a double-stranded DNA with a size of 5,500 nucleotides. These results were quite similar to those of other densoviruses (DNVs). The CSSV had five structural proteins (VP1: 52 KDa, VP2: 56 KDa, VP3: 79 KDa, VP4: 82 KDa, and VP5: 105 KDa). The SDS-PAGE profile of these proteins was quite different from that of the cockroach DNV previously reported and was rather similar to that of Bombyx mori (Bm) DNV-1. An immunochemical study, however, demonstrated that there was no immunological relationship between the CSSV and the Bm DNV-1. These data suggest that the CSSV is a new member of DNV.

Microsatellite instability in sporadic endometrial carcinoma

BACKGROUND

Recent studies have demonstrated ubiquitous somatic microsatellite mutations in some cancers of the colon, endometrium, stomach, and pancreas.

PURPOSE

Our purpose was to characterize the frequency and nature of this replication error (RER) or mutator phenotype in sporadic endometrial carcinoma.

METHODS

Formalin-fixed, paraffin-embedded normal and tumor tissues from 45 patients with sporadic endometrial cancer were screened for the RER phenotype at three microsatellite loci. To further characterize when these alterations were acquired relative to clonal expansion, the sizes of the altered microsatellites in different tumor and normal regions were determined using selective UV radiation fractionation. Approximately 150-300 histologically defined cells on stained tissue sections were covered with small ink dots, and UV irradiation was used to destroy the DNA of cells not covered by ink. Undamaged DNA from seven to 25 spots per section were extracted, then analyzed at the Mfd27, Mfd41, and Mfd47 microsatellite loci and also at the c-K-ras gene locus with individual polymerase chain reactions. Radioactively labeled amplified DNAs were analyzed by electrophoresis and autoradiography. Fisher's exact test and the logrank test were used for statistical analysis.

RESULTS

The RER positive (RER+) phenotype was detected in nine (20%) of 45 sporadic endometrial carcinomas. The topographic tissue distributions of the altered microsatellites revealed clues to their pathogenesis. The RER+ phenotype was homogeneously present in the primary tumors and their metastases and was absent from adjacent normal and hyperplastic endometrium. The altered microsatellites were predominantly the same sizes throughout five tumors but demonstrated greater intratumor heterogeneity in three tumors. In one case, the primary tumor was stable but its metastasis was unstable. Mutant c-K-ras alleles were significantly more frequent in RER+ (56%) than in RER negative (RER-) (14%) tumors (P = .0165) and appeared to be acquired after the RER+ phenotype in one tumor. There were no significant clinical differences between the RER+ and RER- tumors.

CONCLUSIONS AND IMPLICATIONS

The RER+ phenotype is frequently present in sporadic endometrial cancers and is expressed before and during clonal expansion. The underlying mutator mutations are probably heterogeneous, since the RER+ phenotypes were diverse. The absence of altered microsatellites in adjacent normal endometrium demonstrates that the expression of the RER+ phenotype is limited to neoplastic tissue. The bulk of the microsatellite alterations appeared to be acquired prior to clonal expansion, suggesting that expression of the underlying genomic instability contributes to, and is not a consequence of, transformation.

[Effects of metalloproteinases-1 (TIMP-1) cDNA transfection on biological behaviors of PG cells]

A recombinant plasmid, which contains a full length cDNA of human tissue inhibitor of metalloproteinases-1 (TIMP-1), was constructed by using gene recombinant technique, and introduced into a highly metastatic human giant cell carcinoma (PG) by lipofectin technique. Two of the transfectants, PG-T2 and PG-T4, were studied thoroughly. Northern blot showed an increased level of TIMP-1 mRNA in PG-T2 and PG-T4, compared with PG and PG-MV1 (vector-transfected control). The two transfectants also exhibited higher TIMP-1 protein activities. Moreover, they showed significant reduction in their proliferation rate and invasive abilities. The abilities of forming colonies in soft agar and tumorigenecity in athymic nude mice were abrogated in PG-T2 and PG-T4. The preliminary results suggest that a specific upregulation of TIMP-1 expression in metastatic cells could not only suppress their invasive and metastatic phenotype, but also inhibit their proliferation and tumorigenecity.

[Clinicopathological analysis of rhabdomyosarcoma of the ocular adenexa]

12 cases including 11 males and 1 female of rhabdomyosarcoma of ocular adenexa were analysed. The average age of the patients was 4.2 years. 9 cases of lesion were located in the orbit, 2 in the eyelid and 1 in conjunctiva. Pathologically 8 cases were embryonal forms, 2 alveolar, 2 polymorphic. Immunohistochemical studies were performed in 8 cases, which showed desmin positive. Myoglobin presented strong or weak positive in 5 cases, suspicious positive in 3 cases. The clinical manifestation, prognosis and treatment were briefly discussed.

Effect of nucleosides and a nucleotide mixture on proliferation of human gastric cancer cells (KATO III)

The effect of the nucleotides and a nucleotide mixture (OG-VI), consisting of inosine, guanosine 5'-monophosphate (5'-GMP), cytidine, uridine, thymidine (TdR) (4:4:4:3:1 in molar ratio), and TdR co-administration on proliferation of KATO III human gastric cancer cells in culture was evaluated. Consumption of purine and pyrimidine by cancer cells and changes in cell number with OG-VI or TdR were compared with the control culture medium (Williams E) after 72 hour-culture. Addition of OG-VI or TdR did not enhance the cellular proliferation, but inhibited growth when given in higher concentrations (0.3-3 mM inosine, 0.3-3 mM 5'-GMP, 0.22-2.2 mM uridine, 74-740 microM TdR). Consumption rate of TdR in the medium was less in the TdR group, 33.7%, than in the OG-VI group, 72.2% (p < 0.05). This suggests that TdR metabolism is modulated by other nucleosides and nucleotide included in OG-VI. Under the coadministration of 5-fluorouracil (FUra), addition of OG-VI or TdR suppressed cellular proliferation (p < 0.05). The inhibition rate of cellular proliferation in the OG-VI group was slightly higher than the TdR group, but there was no statistically significant difference between the two groups. The combination of FUra with OG-VI or TdR enhances the antitumor effect of FUra. It is concluded that the OG-VI does not enhance the tumor cell proliferation and it is a potential biochemical modulator of FUra metabolism in human cancer cells.

Source of catalysis in the lactate dehydrogenase system. Ground-state interactions in the enzyme-substrate complex

The Raman spectra of both the NAD-pyruvate and the pyridine aldehyde adenine dinucleotide (PAAD)-pyruvate bound to pig heart, pig muscle, and Bacillus stearothermophilus lactate dehydrogenases were measured and are nearly the same, which is consistent with the conserved shell of residues surrounding the active-site cavity in these enzymes. The symmetrical stretching mode of the pyruvate carboxylate group, found at 1398 cm-1, is shifted only slightly when complexed to these enzymes, which shows that the group remains ionized in the ion pair complex with Arg-171 on the enzyme. The vibrational mode for the carbonyl stretch of the bound pyruvate moiety is shifted about 35 cm-1 to a lower frequency than observed for the carbonyl of unliganded pyruvate in the bacterial enzyme because of polarization of the carbonyl bond. Thus, the bacterial enzyme shows the same substrate activation because of the C(+)-O- charge separation that was seen previously with the mammalian enzymes. On the basis of an empirical Badger-Bauer relationship between frequency shift and interaction enthalpy, this shift in frequency is equivalent to an approximately -14 to -17 kcal/mol interaction between the enzyme and the adduct C = O coordinate, a substantial part of which is an electrostatic interaction (hydrogen bond) between the C V O and the protonated His-195. Thus, while the C = O bond is polarized on the enzyme (which requires energy), the overall ground-state enthalpy of the carbonyl imidazolium part of the reaction coordinate is stability substantially relative to its value in solution, and this is the dominant enthalpic effect on the entire reaction coordinate since the other internal coordinates for the hydride transfer are not much affected during formation of the ternary complex.(ABSTRACT TRUNCATED AT 250 WORDS)

[Effect of nitrendipine on hypoxic myocardial energy preservation]

To investigate the relationship between post-hypoxic myocardial dysfunction and myocardial energy reserve and the effect of nitrendipine on hypoxic myocardial energy preservation, we submitted the Langendorff isolated perfused rat hearts to 30 minutes of hypoxia and then 20 minutes of reoxygenation. Nitrendipine was infused continuously 10 minutes before hypoxia and throughout the following perfusion. The high energy phosphate contents of isolated perfused rat hearts before and 30 minutes after hypoxia were measured by using reverse high performance liquid chromatography. The results showed that nitrendipine, when administered prophylactically, enhanced myocardial energy reserve and relieved high energy phosphates' depletion during 30 minutes of hypoxia insult. It is suggested that nitrendipine has an effect on hypoxic myocardial energy preservation.

[Promotion of wound healing with fibroblast growth factor in combined burn radiation injury]

Rats were subjected to 15% burn and severe radiation injury. Recombinant bFGF and simple support treatment were used to treat local wound and total body injury. The results indicated that wound healing was improved by 28.5%, and the time required for 50% area of healing was 9 days earlier in the treated group than control group 60 days after injury. Pathological observation showed that bFGF stimulated proliferation of fibroblast and collagen synthesis. It improved regeneration of capillary and formation of granulation tissue. In the early phase, bFGF enhanced reactive inflammation in the wound and phagocytosis of leucocytes in the body, and enhanced recovery of natural killing activity of spleen cells. These reactions would be beneficial to local wound healing.

[Screening of anti-inflammatory, immunosuppressive and antifertility components of Tripterygium wilfordii V. Effects of 7 diterpene lactone epoxide compounds on the proliferation of T and B lymphocytes in vitro]

The inhibitory effects and their IC50 values of Tripterygium wilfordii (TW) on T and B lymphocytes were assayed using mice splenocytes induced to proliferate by mitogens ConA and LPS in vitro. The results indicated that 6 compounds (T4,T7,T8,T9,T10,L2) and component T1 had significant inhibitory effects on the proliferation of lymphocytes in response to ConA and LPS. The inhibitory potencies of these compounds were in the range of 10(-5)-10(-9) micrograms/ml for both T and B cells, while those of T1 were 3.5 and 4.2 micrograms/ml, respectively. The IC50 values, from low to high, were in the following order: T10,T4,T8,L2,T7,T9 and T1, The dose-effect curves for LPS were to the right of ConA curves, though both were nearly parallel. The relative order of the IC50 values determined from ConA and LPS curves were also coincident. Another compound, T11, showed no suppressive effect on the proliferation of T and B lymphocytes induced by either mitogen, even when its concentration reached 50 micrograms/ml. The results suggest that the suppressive effects of the componends on the proliferation of T and B lymphocytes in vitro were direct and non-selective.

c-k-ras and p53 mutations occur very early in adenocarcinoma of the lung

The topographical distribution of a mutation provides insight into past patterns of tumor evolution. This approach was applied to two loci commonly mutated in adenocarcinoma of the lung--p53 and c-K-ras. In 41 primary adenocarcinomas, c-K-ras codon 12 point mutations were detected in 8 (19.5%) tumors and p53 point mutations were detected in 10 (24.4%) tumors, with one tumor harboring both mutations. These mutations were only detected in malignant cells and with a homogeneous topographical distribution throughout 16 tumors, including metastasis. Intratumor heterogeneity was detected in only one tumor in which a small portion lacked the specific p53 mutation. Based on this topographical analysis, it is likely that when these mutations occur in adenocarcinoma of the lung, they are usually acquired during the very earliest phases of tumor formation before the bulk of clonal expansion, and in very small precursor lesions.

Loss of heterozygosity on chromosome 13 is common only in the biologically more aggressive subtypes of ovarian epithelial tumors and is associated with normal retinoblastoma gene expression

We examined the frequencies of loss of heterozygosity on chromosome 13 in 77 primary ovarian epithelial tumors subdivided into cystadenomas, tumors of low malignant potential, low grade carcinomas, and high grade carcinomas. Such losses were found in approximately 50% of high grade carcinomas but were not detected in any of the other tumor subtypes (P < 0.0001), suggesting a strong association between these abnormalities and the high grade carcinoma phenotype. The tumors were also examined for abnormalities in expression of the retinoblastoma susceptibility gene (RB). This was assessed by immunohistochemical staining of archival tumor sections with a polyclonal antibody directed against both the phosphorylated and the underphosphorylated forms of the RB protein. Most of the tumors, including those with allelic deletions on chromosome 13, showed normal RB nuclear protein staining patterns. We conclude that loss of RB expression is not a frequent event in primary ovarian carcinomas and that this gene is probably not the target of the frequent allelic deletions on chromosome 13 found in high grade ovarian carcinomas.

Vascular development and heparin-binding growth factors in the bovine corpus luteum at several stages of the estrous cycle

Immunolocalization of factor VIII (a specific endothelial cell marker) and heparin-binding (fibroblast) growth factors (HBGF)-1 and HBGF-2, along with quantitative image analysis, were used to evaluate vascular development and distribution of HBGF in the bovine corpus luteum (CL) at three stages (early, middle, and late) of the estrous cycle. Luteal vascularity increased from the early to the middle stage and then declined to the late stage. During the early stage, most of the microvessels were present in the cores of the tissue infoldings (presumably thecal-derived areas), but numerous capillary sprouts could be seen invading the parenchymal areas. During the middle stage, capillary density was so great that most parenchymal cells were in contact with one or more capillaries. At the late stage, relatively few capillaries were present in the parenchymal areas, whereas larger microvessels were prominent throughout the CL. Throughout the estrous cycle, HBGF-1 and HBGF-2 were present primarily in the cytoplasm of large and small luteal cells. For each stage of the estrous cycle, HBGF-2 staining was greater than that of HBGF-1. Relatively high levels of HBGF-2, but not HBGF-1, were also present in connective tissue tracts. In addition, HBGF-1 and HBGF-2 appeared to co-localize in some luteal cells. Although the distribution of HBGF-1 was homogeneous throughout the CI, that of HBGF-2 was heterogeneous. For HBGF-1, staining increased from the early to the middle stage but remained unchanged from the middle to the late stage. In contrast, HBGF-2 staining was greatest in the middle stage and similar in the early and late stages. These data are the first report of HBGF-1 and HBGF-2 immunolocalization in bovine luteal tissues throughout the estrous cycle, and demonstrate that HBGF-2 staining follows a pattern similar to that of luteal vascular development.

Fetal hippocampal transplants reduce aberrant mossy fiber sprouting after CA3 pyramidal cell damage

The CA3 pyramidal cells receive mossy fibers from the dentate granule cells, and the damage to CA3 pyramidal cells induces aberrant mossy fiber sprouting near the site of normal targets. Fetal CA1 and CA3 subregions were separately transplanted into the host CA3 subfield, where CA3 pyramidal neurons were previously damaged with kainic acid. In vitro [3H]inositol 1,4,5-trisphosphate (IP3) receptor autoradiography was used to analyze the purity of CA1 neurons. CA1 transplants had high IP3 receptor density compatible with adult CA1 subfield, while CA3 transplants had trace IP3 receptors. Animals with successful graft-host connections exhibited no aberrant mossy fiber sprouting, and mossy fibers invaded into the fetal CA3 grafts. However, animals without direct host mossy fibers-grafts connection showed aberrant mossy fiber sprouting in the CA3 subfield. These observations demonstrate that aberrant mossy fiber sprouting was suppressed by molecular cues presented on the grafted neurons and that [3H]IP3 receptor autoradiography provides an excellent marker for the identification of the CA1 pyramidal cells in grafts.

Crystal structures of the myristylated catalytic subunit of cAMP-dependent protein kinase reveal open and closed conformations

Three crystal structures, representing two distinct conformational states, of the mammalian catalytic subunit of cAMP-dependent protein kinase were solved using molecular replacement methods starting from the refined structure of the recombinant catalytic subunit ternary complex (Zheng, J., et al., 1993a, Biochemistry 32, 2154-2161). These structures correspond to the free apoenzyme, a binary complex with an iodinated inhibitor peptide, and a ternary complex with both ATP and the unmodified inhibitor peptide. The apoenzyme and the binary complex crystallized in an open conformation, whereas the ternary complex crystallized in a closed conformation similar to the ternary complex of the recombinant enzyme. The model of the binary complex, refined at 2.9 A resolution, shows the conformational changes associated with the open conformation. These can be described by a rotation of the small lobe and a displacement of the C-terminal 30 residues. This rotation of the small lobe alters the cleft interface in the active-site region surrounding the glycine-rich loop and Thr 197, a critical phosphorylation site. In addition to the conformational changes, the myristylation site, absent in the recombinant enzyme, was clearly defined in the binary complex. The myristic acid binds in a deep hydrophobic pocket formed by four segments of the protein that are widely dispersed in the linear sequence. The N-terminal 40 residues that lie outside the conserved catalytic core are anchored by the N-terminal myristylate plus an amphipathic helix that spans both lobes and is capped by Trp 30. Both posttranslational modifications, phosphorylation and myristylation, contribute directly to the stable structure of this enzyme.

Histologically benign or low-grade malignant tumors adjacent to high-grade ovarian carcinomas contain molecular characteristics of high-grade carcinomas

It is presently not clear if ovarian carcinomas arise de novo or from benign precursors (cystadenomas) and if high-grade malignant tumors (carcinomas) develop from preexisting low-grade carcinomas. The presence of allelic losses on chromosome 11p15.5 distinguishes high-grade ovarian carcinomas from either low-grade carcinomas or cystadenomas. We therefore examined the distribution of such losses in different parts of heterogeneous tumors showing mixed histological grades or showing adjacent large histologically benign neoplasms. The results showed that all neoplastic areas, including those that were histologically benign or compatible with low-grade carcinomas, contained allelic losses at the above locus. This suggests that the morphologically less aggressive portions of these heterogeneous tumors were not typical cystadenomas or low-grade carcinomas and contained molecular abnormalities indicative of at least a predisposition to the high-grade carcinoma phenotype.

p53 gene mutations in Chinese human testicular seminoma

Genomic deoxyribonucleic acid from 17 primary human testicular seminomas was screened for the presence of mutations in exons 5 to 8 of gene p53, using the single strand conformation polymorphism assay, followed by direct deoxyribonucleic acid sequencing. The p53 mutations in 1 allele leading to an amino acid change but a normal (wild-type) sequence in the remaining allele were identified in 4 of 17 seminomas (23.5%). Sites of mutations were in exon 5 (codon 141), exon 7 (codon 238, codon 258) and exon 8 (codon 270). The present study suggested that mutation of the p53 gene is involved in the development of human testicular seminoma as in the case of several other types of human cancers.

Structure of the complex between pyridoxal 5'-phosphate and the tyrosine 225 to phenylalanine mutant of Escherichia coli aspartate aminotransferase determined by isotope-edited classical Raman difference spectroscopy

The azomethine (Schiff base) linkage between the epsilon-amino group of active-site lysine 258 and the carbonyl moiety of enzyme-bound pyridoxal 5'-phosphate (PLP) normally exhibits absorbance maxima at ca. 360 (high-pH form) or ca. 430 nm (low-pH form). However, the absorbance maximum is shifted from 358 to 386 nm, a value which is similar to that of free PLP (lambda max = 388 nm), in a mutant form of Escherichia coli aspartate aminotransferase (AATase) in which tyrosine 225, which normally donates a hydrogen bond to the phenolate function of PLP, has been replaced with phenylalanine (Y225F). This spectral shift suggested that PLP binds to Y225F as the free aldehyde. The following evidence from isotope-edited classical Raman spectroscopy proves conclusively that the near-UV spectrum is anomalous and that PLP is bound to Y225F as a Schiff base: (1) A strong cofactor peak at 1630 cm-1 in the holoenzyme-minus-apoenzyme difference spectrum of the unprotonated form of Y225F is red-shifted by 18 cm-1 in enzyme labeled with 15N at lysine 258 and other positions. (2) This isotope-induced red shift is similar to that observed in the unprotonated form of the model Schiff base, PLP-valine. (3) The Raman spectrum of Y225F is unchanged in H(2)18O, while peaks at ca. 1670 cm-1 in the spectrum of free PLP or in that of a mutant of AATase in which Lys-258 is replaced with Ala, are red-shifted by ca. 30 cm-1 in H(2)18O.(ABSTRACT TRUNCATED AT 250 WORDS)

Structure of the mammalian catalytic subunit of cAMP-dependent protein kinase and an inhibitor peptide displays an open conformation

The crystal structure of a binary complex of the porcine heart catalytic (C) subunit of cAMP-dependent protein kinase (space group P4(1)32; a = 171.5 A) complexed with a di-iodinated peptide inhibitor, PKI(5-24), has been solved and refined to 2.9 A resolution with an overall R of 21.1%. The r.m.s. deviations from ideal bond lengths and angles are 0.022 A and 4.3 degrees. A single isotropic B of 17 A(2) was used for all atoms. The structure solution was carried out initially by molecular replacement of electron density followed by refinement against atomic coordinates from orthorhombic crystals of a binary complex of the mouse recombinant enzyme previously described [Knighton, Zheng, Ten Eyck, Ashford, Xuong, Taylor & Sowadski (1991). Science, 253, 407-414]. The most striking difference between the two crystal structures is a large displacement of the small lobe of the enzyme. In the cubic crystal, the beta-sheet of the small lobe is rotated by 15 degrees and translated by 1.9 A with respect to the orthorhombic crystal. Possible explanations for why this binary complex crystallized in an open conformation in contrast to a similar binary complex of the recombinant enzyme are discussed. This study demonstrates that considerable information about parts of a crystal structure can be obtained without a complete crystal structure analysis. Specifically, the six rigid-group parameters of a poly alanine model of the beta-structure were obtained satisfactorily from a crystal structure by refinement of difference Fourier coefficients based on an approximate partial structure model.

A study of the binding of NADP coenzymes to dihydrofolate reductase by raman difference spectroscopy

We report here the Raman spectra of NADPH, NADP+, 3-acetylpyridine adenine dinucleotide (AcPdADP+), NADH and a fragment of these molecules, 2'-phospho-adenosine-5'-diphosphoribose (Ado2'p5'ppRib), bound to Escherichia coli dihydrofolate reductase (DHFR). The positions that are observed for the bound adenosine 'triplet' bands are consistent with a protein binding pocket for this group which is quite hydrophobic in nature. No binding effect is observed on Raman bands associated with the nicotinamide group of NADP+ as a binary complex with DHFR, suggesting very loose, if any, binding of this group. In contrast, changes in the Raman spectrum of the nicotinamide group of NADP+ bound to an inhibitor (trimethoprim) ternary complex of DHFR are clearly observed which indicate substantial binding interaction. The carboxamide group of bound NADPH (and NADH) adopts the trans conformation. A 35-cm-1 upshift is observed in the rocking motion of the carboxamide -NH2 group of NADPH, and a 5-cm-1 upward shift is seen in the C=O stretch mode of AcPdADP+ upon binding to the enzyme-trimethoprim complex. These results suggest that the -NH2 group of the carboxamide moiety is more tightly hydrogen bonded in the protein binding pocket than in solution while that of the C=O group is less tightly hydrogen bonded; these hydrogen bonds would appear to be responsible for holding the nicotinamide headgroup in place properly for catalysis. We have compared this with the results obtained previously in other protein complexes, and interpret the observed shifts in these bands as a measure of the hydrogen bonding enthalpy of the -NH2 and C=O groups with their protein environments. Perhaps surprisingly, the magnitude of the hydrogen bonding enthalpy takes on a limited number of discrete values over five protein complexes rather than over a continuous range. The effect that this has on the catalytic properties of DHFR and the other NAD dehydrogenases that we have studied to date, particularly their stereochemistry, is discussed. A small downward shift is observed for the P = O stretch of the 2'-phosphate moiety of NADP. This indicates that the 2'-phosphate moiety binds to DHFR in the dianionic form. Furthermore, the local enthalpic interaction that the 2'-phosphate group has with protein is stronger than its interaction with water.

cAMP-dependent protein kinase defines a family of enzymes

The structure of the recombinant mouse catalytic subunit of cAMP-dependent protein kinase is reviewed with particular emphasis on the overall features and specific amino acids that are shared by all members of the eukaryotic protein kinase family. The crystal structure of a ternary complex containing both MgATP and a twenty-residue inhibitor peptide defines the precise role of the conserved residues that are clustered at the active site. In addition to catalysing the post-translational modification of other proteins, the catalytic subunit is itself subject to covalent modifications. It is a phosphoprotein and is also myristylated at its amino terminus. The enzyme when crystallized in the presence of detergent shows a detergent molecule bound to an acyl pocket that is presumably occupied by the myristyl moiety in the mammalian enzyme. When expressed in E. coli, the catalytic subunit is autophosphorylated at four sites. Two stable phosphates at Ser338 and Thr197 interact with multiple protein side chains thus explaining why they are inaccessible to phosphatases. Although all substrates and inhibitors of the catalytic subunit share a general minimum consensus sequence, the high affinity binding of protein inhibitors such as the regulatory subunits and the heat stable protein kinase inhibitors require additional determinants that lie beyond the consensus site. These two physiological inhibitors of the catalytic subunit appear to use different sites to achieve high-affinity binding.

Structural features that specify tyrosine kinase activity deduced from homology modeling of the epidermal growth factor receptor

To identify structural features that distinguish protein-tyrosine kinases from protein-serine kinases, a molecular model of the kinase domain of epidermal growth factor receptor was constructed by substituting its amino acid sequence for the amino acid sequence of the catalytic subunit of cAMP-dependent protein kinase in a 2.7-A refined crystallographic model. General folding was conserved as was the configuration of invariant residues at the active site. Two sequence motifs that distinguish the two families correspond to loops that converge at the active site of the enzyme. A conserved arginine in the catalytic loop is proposed to interact with the gamma phosphate of ATP. The second loop provides a binding surface that positions the tyrosine of the substrate. A positively charged surface provides additional sites for substrate recognition.

[Pathologic, electron microscopic and experimental examination of band keratopathy]

One hundred and thirteen cases previously diagnosed as band keratopathy were reexamined by light microscopy and histochemistry, 10 cases of which were studied by TEM and 2 cases were studied by SEM. We find that the calcium deposition initially occur as fine calcific particles within the cytoplasm of epithelic cells and in the basal membrane and bowman's layer, which aggregated to form calcific spherules and large calcific masses extracellularly. When 3 normal corneal tissues were frozen and cultured, the calcium deposition occur in the superficial layer of bowman's membrane and in the stromal lamellae, Authors suggest that the degeneration and calcific abnormal metabolism of the cell caused by various factors is the main pathogenesis that leads to the calcific deposit. The evaporation and constructive destruction of the corneal surface in the interpiperbral area inhibits the formation of the lacrimal membrane and results in deposition of calcium salts in the superficial tissue of exposed cornea in a band configuration. The combination of glycosaminoglycan with calcium salts is the dynamics of aggregation of the fine calcific particles to form the calcific spherules and calcific masses.

2.0 Å refined crystal structure of the catalytic subunit of cAMP-dependent protein kinase complexed with a peptide inhibitor and detergent

. A mutant (Serl39Ala) of the mouse recombinant catalytic (C) subunit of cAMP-dependent protein kinase was co-crystallized with a peptide inhibitor, PKI(5-24), and MEGA-8 (octanoyl-N-methylglucamide) detergent. This structure was refined using all observed data (30 248 reflections) between 30 and 1.95 A resolution to an R factor of 0.186. R.m.s. deviations of bond lengths and bond angles are 0.013 A and 2.3 degrees, respectively. The final model has 3075 atoms (207 solvent) with a mean B factor of 31.9 A(2). The placement of invariant protein-kinase residues and most C:PKI(5-24) interactions were confirmed, but register errors affecting residues 55-64 and 309-339 were corrected during refinement by shifting the affected sequences toward the C terminus along the previously determined backbone path. New details of C:PKI(5-24) interactions and the Ser338 autophosphorylation site are described, and the acyl group binding site near the catalytic subunit NH(2) terminus is identified.

2.2 A refined crystal structure of the catalytic subunit of cAMP-dependent protein kinase complexed with MnATP and a peptide inhibitor

. The crystal structure of a ternary complex containing the catalytic subunit of cAMP-dependent protein kinase, ATP and a 20-residue inhibitor peptide was refined at a resolution of 2.2 A to an R value of 0.177. In order to identify the metal binding sites, the crystals, originally grown in the presence of low concentrations of Mg(2+), were soaked in Mn(2+). Two Mn(2+) ions were identified using an anomalous Fourier map. One Mn(2+) ion bridges the gamma- and beta-phosphates and interacts with Asp184 and two water molecules. The second Mn(2+) ion interacts with the side chains of Asn171 and Asp l84 as well as with a water molecule. Modeling a serine into the P site of the inhibitor peptide suggests a mechanism for phosphotransfer.

Initial characterization of endothelial mitogens produced by bovine corpora lutea from the estrous cycle

To further characterize mitogenic factor(s) present in luteal extracts or luteal explant conditioned media (LCM), bovine corpora lutea (CL) were homogenized or incubated in explant culture, respectively. After evaluation of luteal extracts and LCM by using an endothelial cell proliferation bioassay, mitogenic activity was characterized by immunoneutralization with antibodies against heparin-binding (fibroblast) growth factor (HBGF) 1 or 2. LCM also were subjected to ultrafiltration, as well as anion-exchange, cation-exchange, and heparin-affinity chromatography. The presence of HBGF-2 in LCM also was evaluated by using a dot immunoblot assay. Extracts of luteal tissues and LCM stimulated (P < 0.05) proliferation of endothelial cells in a dose-dependent manner. Mitogenic activity of luteal extracts and LCM was decreased (P < 0.05) by treatment with specific antibodies against HBGF-2 or HBGF-1. LCM also contained immunoreactive HBGF-2. The mitogenic activity bound to anion exchangers, phenyl-Sepharose, and heparin-agarose, but not to cation exchangers, indicating that endothelial mitogenic activity is anionic at neutral pH, has some hydrophobic characteristics, and belongs to the HBGF family of proteins. Following ultrafiltration, endothelial mitogenic activity was retained by membranes having a 30,000 or 100,000 molecular weight cutoff. In addition, LCM was resolved into four peaks of heparin-binding endothelial mitogenic activity, each with a different affinity for heparin. These data demonstrate that bovine CL contain and produce endothelial mitogens of large molecular size, which may be important regulators of luteal function. These endothelial mitogens are heparin-binding and anionic at neutral pH.(ABSTRACT TRUNCATED AT 250 WORDS)

Investigation of microtubule assembly and organization accompanying tension-induced neurite initiation

Pulling on the margin of embryonic chick sensory neurons induces neurite formation de novo. We find that these neurites contain microtubules within minutes after the application of tension and apparently normal microtubule arrays within 10–20 min. We wished to determine whether these microtubules reflected existing microtubules that were reorganized, e.g. pulled into the neurite by the applied forces, or whether they reflected primarily new assembly of tubulin. We investigated tension-induced neurite initiation in the presence of 4 nM vinblastine, a concentration that poisons net microtubule assembly but does not depolymerize extant polymers, thus separating new assembly from movements of existing microtubules. We find that vinblastine seriously compromises the ability of chick sensory neurons to initiate neurites in response to tension. The few poisoned neurites that did form were abnormal in several respects. In contrast to unpoisoned cells, poisoned neurites were prone to stretching and breaking while pulling, as though they lacked normal structural support. Indeed, poisoned neurites possessed only short microtubule fragments. We conclude that the microtubule array seen in tension-induced neurites reflects primarily new microtubule assembly, rather than existing microtubules that were reorganized to invade the neurite. This implies that tension applied to unpoisoned chick sensory neurons rapidly stimulates new microtubule assembly concomitant with neurite initiation. Examination of the tension-induced microtubules shows that both their spatial pattern and their acetylation are similar to that reported for normal growth cone-mediated neurites.

Crystal structure of the catalytic subunit of cAMP-dependent protein kinase complexed with MgATP and peptide inhibitor

The structure of a ternary complex of the catalytic subunit of cAMP-dependent protein kinase, MgATP, and a 20-residue inhibitor peptide was determined at a resolution of 2.7 A using the difference Fourier technique starting from the model of the binary complex (Knighton et al., 1991a). The model of the ternary complex was refined using both X-PLOR and TNT to an R factor of 0.212 and 0.224, respectively. The orientation of the nucleotide and the interactions of MgATP with numerous conserved residues at the active site of the enzyme are clearly defined. The unique protein kinase nucleotide binding site consists of a five-stranded antiparallel beta-sheet with the base buried in a hydrophobic site along beta-strands 1 and 2 and fixed by hydrogen bonds to the N6 amino and N7 nitrogens. The small lobe secures the nucleotide via a glycine-rich loop and by ion pairing with Lys72 and Glu91. While the small lobe fixes the nontransferable alpha- and beta-phosphates in this inhibitor complex, the gamma-phosphate is secured by two Mg2+ ions and interacts both directly and indirectly with several residues in the large lobe--Asp184, Asn171, Lys168. Asp166 is positioned to serve as a catalytic base. The structure is correlated with previous chemical evidence, and the features that distinguish this nucleotide binding motif from other nucleotide binding proteins are delineated.

The natural history of dry type of age-related macular degeneration

To study the natural history of dry type of age-related macular degeneration (AMD) and search for a sensitive method for detecting the development of the disease, the fundus fluorescein angiography, visual acuity, electroretinogram and FM 100-hue test were used to examine 75 eyes, 147 eyes, 73 eyes, and 94 eyes respectively. These examinations were taken at least twice during the follow-up periods. The average age was 63.2 years (50-80 years). The average follow-up was 29.8 months with a range of 3-74 months. It was shown tht there were not any statistically significant difference in the macular lesions and electroretinogram between the initial examinations and after follow-up (P > 0.05). 91.14% of the eyes maintained good visual acuity during the follow-up. Subretinal neovascularization developed only in one of the eyes. The total error score of FM 100-hue test had a statistically significant difference between the initial test and the test taken two years afterwards (P < 0.01). It was suggested that most of the dry type of AMD had a favorable prognosis and that color visual test was a sensitive method for monitoring the development of dry type of AMD.

A template for the protein kinase family

The crystal structure of the catalytic subunit of cAMP-dependent protein kinase, complexed with ATP and a 20-residue inhibitor peptide, is reviewed and correlated with chemical and genetic data. The striking convergence of the structure with the biochemistry and genetics provides for the first time a molecular basis for understanding how this enzyme functions, as well as an explanation for the highly conserved residues that are scattered throughout the molecule. Because these residues probably serve a common role in all eukaryotic protein kinases, this first protein kinase structure serves as a general template for the entire family of enzymes.

Dynamic investigation on chromosome aberration of a human retinoblastoma cell line So-Rb50

G-banding and karyotype analyses of cells in seventeen passages of SO-Rb50 during a long period of culture for about four years were performed. Three chromosome markers 13q14-, 1p36+ and 12p13+ were found. Cells possessed 13q14- reduced to zero after the 200th passage while 1p+ and 12p+ cells increased to 100% after 30 and 200 passages respectively. Abnormal chromosomes, ring chromosomes, chromosome radiuses and double minutes were also observed. These chromosomal changes were more often seen before the 200th passage. The significance of these changes are discussed.

Identification of covalent adducts to protein sulfur nucleophiles by alkaline permethylation

We recently reported on the identification of metabolites of the hepatotoxin bromobenzene covalently bound to rat liver protein sulfur nucleophiles (D. E. Slaughter and R. P. Hanzlik, Chem. Res. Toxicol. 4, 349-359 (1991). Central to that study was our development of a method called alkaline permethylation which converts protein-S adducts of xenobiotic electrophiles to stable extractable thioanisole derivatives. We report here on substantial improvements to our original alkaline permethylation method which should greatly expand its potential utility. Specifically, we have developed significantly milder reaction conditions, eliminated side reactions, improved the amount of and consistency of thioanisole yields from various mercapturic acid model compounds, and increased the overall sensitivity of the method at least 50-fold. Using the procedure described herein it is routinely possible to generate, detect, and identify by GC/MS as little as 2 pmol of a thioanisole derivative. This method is potentially quite general and should prove useful for studies in the toxicology of reactive metabolites, for industrial hygiene and biomonitoring, and for agrichemical residue analysis.

Structure of hepatitis B virus core and e-antigen. A single precore amino acid prevents nucleocapsid assembly

The hepatitis B virus core gene codes for two polypeptides: the core protein, which assembles to form particles (HBcAg), and the secreted precore protein (HBeAg). Expression vectors directing the synthesis in Escherichia coli of a recombinant HBeAg corresponding in sequence to serum-derived HBeAg encompassing the 10 precore amino acids remaining after cleavage of the precursor and residues 1-149 of HBcAg (PC-HBeAg) were constructed. Recombinant PC-HBeAg, HBcAg, and C-terminally truncated HBcAg were isolated from E. coli and analyzed by sucrose velocity sedimentation, electron microscopy, anti-HBc/e specific monoclonal antibody analysis, and for immunogenicity. HBcAg and truncated HBcAg formed 27-nm particles and displayed HBc antigenicity. In contrast, PC-HBeAg was nonparticulate and did not band in sucrose gradients. PC-HBeAg was recognized efficiently by HBeAg-specific antibodies and displayed little HBc antigenicity. Immunogenicity studies including T and B cell recognition confirmed that PC-HBeAg demonstrates HBe antigenicity. The presence of the 10 precore amino acids therefore prevented particle formation. To analyze which precore amino acids might be responsible for the prevention of particle formation a cysteine to glutamine substitution at amino acid position -7 was introduced into PC-HBeAg (-7C-->Q)PC-HBeAg. This single amino acid change at position -7 restored particle formation and HBc antigenicity. The evolutionarily conserved cysteine at position -7 thus appears responsible for the prevention of particle assembly in the HBeAg biosynthesis pathway.

A weak B antigen with serologic reactivity between B1 and B2 red blood cells found in a Chinese family

During a serologic study on red cell samples from individuals representing three generations of a Chinese family, an unusual pattern of reactivity was noted in a sample from a daughter of an A1B2 individual. The results of direct ABO grouping, titration, and adsorption studies demonstrated that the red blood cells (RBCs) from the proposita and two of the proposita's uncles (1) expressed more B antigen than group B2 RBCs but less than group B1 RBCs; (2) expressed the B1 antigen but at a lower level than group B1 RBCs; and (3) expressed more H antigen than B1 RBCs but slightly less than B2 RBCs. The saliva from the proposita contained soluble B and H antigens, and her serum contained a weak B-gene-specified transferase. Serologic reactivity of her RBCs was intermediate between that of B1 and B2, RBCs. That is similar to reactivity of Aint RBCs, which is intermediate between A, and A2 RBCs. The proposita may represent a Bint phenotype.

Structural framework for the protein kinase family

In this review, we have summarized the general structural features of the catalytic subunit of cAMP-dependent protein kinase, emphasizing those features that will very likely be conserved in all members of the protein kinase family. The overall secondary structure of the catalytic core will probably be conserved throughout the catalytic core, as will the active site regions associated with MgATP binding and catalysis. The mechanisms for activation and the role of protein phosphorylation are unique for each kinase. The structure of the catalytic subunit now provides a general framework for modeling other protein kinases. Although this is no substitute for a crystal structure for each protein kinase, this one structure, nevertheless, does provide major insights to the molecular organization of each of these enzymes.

Spatial buffering of extracellular potassium by Müller (glial) cells in the toad retina

We examined the role of Müller (glial) cells in buffering light-evoked changes in extracellular K+ concentration, [K+]o, in the isolated retina of the toad, Bufo marinus. We found evidence for two opposing Müller cell current loops that are generated by a light-evoked increase in [K+]o in the inner plexiform layer. These current loops, which are involved in the generation of the M-wave of the electroretinogram (ERG), prevent the accumulation of K+ in the inner plexiform layer by transporting K+ both to vitreous and to distal retina. In addition, under dark-adapted conditions, we found evidence for a Müller cell current loop that is generated by a light-evoked decrease in [K+]o in the receptor layer. This current loop, which is involved in the generation of the slow PIII component of the ERG, helps to buffer the light-evoked decrease in [K+]o throughout distal retina by transporting K+ from vitreous. The spatial buffering fluxes of K+ can be abolished by blocking Müller cell K+ conductance with 200 microM Ba2+. The separate contributions of the M-wave and slow PIII currents to Müller cell spatial buffering were isolated by various pharmacological treatments that were designed to enhance or suppress light-evoked activity in specific retinal neurons. Our results show that Müller cell K+ currents not only buffer light-evoked increases in [K+]o, but also buffer light-evoked decreases in [K+]o, and thereby diminish any deleterious effects upon neuronal function that could arise in response to large changes in [K+]o in the plexiform layers. Moreover, our results emphasize that spatial buffering currents generate many components of the electroretinogram.

Bromo(monohydroxy)phenyl mercapturic acids. A new class of mercapturic acids from bromobenzene-treated rats

Alkaline permethylation and GC/MS analysis of urinary mercapturic acids from rats given bromobenzene yielded several quinone-derived bromodimethoxythioanisole isomers as expected. Unexpectedly, seven bromomonomethoxythioanisole isomers were also observed, suggesting the presence of bromomonohydroxyphenyl mercapturic acids in the urine. Alkaline permethylation of synthetic 4- and 5-bromo-2-hydroxyphenyl mercapturic acid gave 4- and 5-bromo-2-methoxythioanisole, respectively, which were also observed after alkaline permethylation of urine from bromobenzene-treated rats, as was 2-bromo-4-methoxythioanisole. To explore the biosynthetic origin of the bromonohydroxyphenyl mercapturic acids, rats were separately dosed intraperitoneally with synthetic racemic 2-, 3-, or 4-bromophenyl mercapturic acid, or biosynthetic L-(-)-4-bromophenyl mercapturic acid, or a biosynthetic mixture of the 3,4- and 4,3-premercapturic acids from bromobenzene, and their urine (0-24 hr) analyzed by alkaline permethylation and GC/MS. The administered mercapturic acids and premercapturic acids were partly excreted unchanged (60-80% and 24%, respectively), but both gave rise to bromomonohydroxyphenyl mercapturic acids (0.1-5.2% of dose). Results indicated that the latter could be formed by 1) dehydrogenation of premercapturic acids and 2) hydroxylation of mercapturic acids (or their cysteine equivalents).