Synthesis and degradation of 1-aminocyclopropane-1-carboxylic acid by Penicillium citrinum

1-Aminocyclopropane-1-carboxylic acid (ACC), which is a precursor of ethylene in plants, has never been known to occur in microorganisms. We describe the synthesis of ACC by Penicillium citrinum, purification of ACC synthase [EC 4.4.1.14] and ACC deaminase [EC 4.1.99.4], and their properties. Analyses of P. citrinum culture showed occurrence of ACC in the culture broth and in the cell extract. ACC synthase was purified from cells grown in a medium containing 0.05% L-methionine and ACC deaminase was done from cells incubated in a medium containing 1% 2-aminoisobutyrate. The purified ACC synthase, with a specific activity of 327 milliunit/mg protein, showed a single band of M(r) 48,000 in SDS-polyacrylamide gel electrophoresis. The molecular mass of the native enzyme by gel filtration was 96,000 Da. The ACC synthase had the Km for S-adenosyl-L-methionine of 1.74 mM and kcat of 0.56 s-1 per monomer. The purified ACC deaminase, with a specific activity of 4.7 unit/mg protein, showed one band in SDS-polyacrylamide gel electrophoresis of M(r) 41,000. The molecular mass of the native ACC deaminase was 68,000 Da by gel filtration. The enzyme had a Km for ACC of 4.8 mM and kcat of 3.52 s-1. The presence of 7 mM Cu2+ in alkaline buffer solution was effective for increasing the stability of the ACC deaminase in the process of purification.

Evaluation of the mouse lymphoma tk assay (microwell method) as an alternative to the in vitro chromosomal aberration test

In order to evaluate the utility of the mouse lymphoma assay (MLA) for detecting in vitro clastogens and spindle poisons and to compare it with the in vitro chromosomal aberration test (CA), we conducted an international collaborative study of the MLA that included 45 Japanese laboratories and seven overseas laboratories under the cooperation of the Ministry of Health and Welfare of Japan and the Japanese Pharmaceutical Manufacturer's Association. We examined 40 chemicals; 33 were reportedly positive in the CA but negative in the bacterial reverse mutation assay, six were negative in both assays and one was positive in both. We assayed mutations of the thymidine kinase (TK) locus (tk) of L5178Y tk +/- mouse lymphoma cells using the microwell method. According to our standard protocol, cells were exposed to the chemical for 3 h, cultured for 2 days and TK-deficient mutants were expressed in 96-well plates under trifluorothymidine. Each chemical was coded and tested by two or three laboratories. Among the 34 CA-positive chemicals, positive MLA results were obtained for 20 and negative results were obtained for nine. The remaining five chemicals were inconclusive or equivocal because of discrepant inter-laboratory results or reproduced discrepant results, respectively. Among the six CA-negative chemicals, one was negative in the MLA, two were positive and three were inconclusive. Thus, the MLA could detect only 59% (20/34) of CA-positive chemicals. We concluded that the MLA was not as sensitive as the CA. Some MLA-negative chemicals evoked positive responses in the CA only after long continuous treatment. These might also be genotoxic in the MLA with long continuous treatment. Improvement of the MLA protocol, including alteration of the duration of the treatment, might render the MLA as sensitive as the CA.

The need for long-term treatment in the mouse lymphoma assay

The L5178Y tk +/- mouse lymphoma assay (MLA) has been widely used as a genotoxicity test for the detection of mutagens and clastogens. The standard MLA, as well as other mammalian cell gene mutation assays, usually employs a short treatment period (3-6 h). Our previous report, however, suggested that such short treatments may be insufficient for detecting some clastogens and spindle poisons. For the present study, we introduced and evaluated a longer treatment (24 h) in the MLA. We examined 15 chemicals which were evaluated as negative or inconclusive in the short-term study. Cells were exposed to the chemical for 24 h without S9 mix, cultured for 2 days and then thymidine kinase-deficient mutants were selected in 96-well microtiter plates under trifluorothymidine. Eleven chemicals yielded positive responses in the 24 h treatment MLA. They included nucleoside analogs (2'-deoxycoformycin and dideoxycytidine), a base analog (1,3-dimethylxanthine) and spindle poisons (colchicine and vinblastine sulfate), all of which do not directly affect DNA, but bring about mutations and chromosome alterations through nucleoside metabolism and chromosome segregation. Because the mutagenicities of these non-DNA targeting chemicals appear to be cell cycle dependent, treatment extending over more than one cell cycle may be required for their effect. Combining results from the present and previous studies, 31 of 34 (91%) chromosome aberration-positive chemicals exhibited positive responses in the MLA, suggesting that the sensitivity of the MLA with 24 h treatment periods approaches that of the chromosome aberration test.

[A 63-year-old man with progressive cauda equina/conus medullaris syndrome]

A 63-year-old man, whose father died of malignant lymphoma, developed subacutely cauda equina/conus medullaris syndrome progressed over 3 months. Initial radicular pain, ascending motor and sensory paralysis without sacral sparing, vesicorectal dysfunction were similar with signs of spinal dural arteriovenous fistula. However, mild inflammatory signs, raised serum LDH, predominantly of LDH 3, lymphocytic pleocytosis and elevated beta 2 microglobulin in CSF suggested neurolymphomatosis. It was not supported, however, after CSF immunocytochemistry, myelogram, CT, Gd-MRI and Ga scan. Spinal cord/nerve root vascular syndromes of intravascular lymphomatosis (IVL) according to Glass J et al. was suspected because of the unique neurological progression similar to Foix-Alajouanine syndrome, hypoxia without abnormalities in chest X-ray film, response to steroids and raised serum soluble IL-2 receptor. Multiple biopsies were performed with negative results. However, after all muscle biopsy confirmed IVL. The lower spinal irradiation was not effective. But CHOP regimen supplemented by granulocyte colony-stimulating factor (G-CSF) brought about swift neurological improvement and protection from late complications. Self-limiting polyneuropathy emerged during the biweekly CHOP therapy, 6 courses for 12 weeks. Eventually he was neurologically improving 10 months after the chemotherapy and adrenal enlargement, which was possibly of metastasis, was only against complete remission. This case was good outcome by biweekly CHOP using G-CSF when compared with very high mortality in reported IVL cases besides vincristine neurotoxicity under compromised blood-brain/nerve barrier due to IVL might affect the functional recovery. This case with IVL implied raised soluble IL-2 receptor and progressive cauda equina syndrome/ascending myelopathy as diagnostic clues, and efficiency of muscle biopsy to confirm IVL.

Specific mutational spectrum of dimethylnitrosamine in the lacI transgene of Big Blue C57BL/6 mice

Dimethylnitrosamine (DMN) produces tumors in mice predominantly in the liver, but also in the kidney and lung. It forms O6-methylguanine adducts in DNA, which induce G:C-->A:T transitions. We have analyzed the spectra of spontaneous and DMN-induced mutations in the lacI transgene of the Big Blue mouse (C57BL/6). In both cases, mutations in the liver, kidney and lung were predominantly base substitutions, among which G:C-->A:T transitions were the most frequent. In contrast, a high incidence of short deletions (2-23 bp) was only found in the liver of treated mice. The deletions often occurred at direct repeat sequences. Single-base deletion incidence was also higher in the liver than in the kidney and lung. These results imply that accumulation of DNA lesions or their repair in liver is different from other organs. Spontaneous and induced base substitutions and deletions appeared to be randomly distributed in the lacI gene and an apparent hotspot was not observed, except for a 4 bp deletion of a (TGGC)3 sequence at positions 621-632. The present data demonstrate, for the first time, that DMN induces short deletions especially in the liver, although the mechanism involved needs further investigation.

Localization of mRNA for inflammatory cytokines in radicular cyst tissue by in situ hybridization, and induction of inflammatory cytokines by human gingival fibroblasts in response to radicular cyst contents

The expression of mRNA encoding the inflammatory cytokines interleukin-1alpha (IL-1alpha), interleukin-1beta (IL-1beta), interleukin-6 (IL-6), interleukin-8 (IL-8) and tumor necrosis factor alpha(TNF-alpha) have been examined in radicular cysts by in situ hybridization. Furthermore, the biological activity of the contents of radicular cysts (RCC) has been assayed by adding extracts of RCC to cultured human gingival fibroblasts (HGFs) and analyzing the culture medium for the release of inflammatory cytokines. In the epithelial layer, keratinocytes expressed all cytokine mRNAs examined at various levels. Basal layer cells expressed mRNA for each cytokine. In the subepithelial granulation tissue of the cysts, fibroblasts and macrophages expressed mRNA for IL-6, IL-8, IL-1beta and TNF-alpha mRNA at varying levels; especially clear expression of TNF-alpha and IL-1beta mRNA was detected on macrophages. The infiltrating lymphoid cells, largely composed of T cells and plasma cells, expressed these cytokine mRNAs, especially those encoding IL-6 and IL-8, at various levels. In vitro analysis indicated dose-dependent release of both IL-6 and IL-8 by HGFs in response to RCC. After heating to 100 degrees C for 10 min, RCC almost completely failed to stimulate IL-6 release from HGFs. Furthermore, anti-IL-1beta antibody (neutralization test) did not prevent the stimulation of IL-6 release by RCC. Significant amounts of IL-6 and IL-8 were detected in RCC in two cases, and a trace amount of IL-1beta was detected in one case. This study demonstrated the wide expression of mRNA encoding inflammatory cytokines in radicular cyst tissues, and RCC itself was capable of stimulating IL-6 and IL-8 production from HGFs.

Cutaneous allergic vasculitis: clinicopathological characterization and identification of apoptosis

To elucidate the clinicopathological features of cutaneous allergic (leukocytoclastic) vasculitis (CAV), biopsied skin tissues of 32 patients with CAV were examined immunohistopathologically and compared with the main clinical features. Additionally, to obtain some clues to better understand the roles of infiltrating cells, particularly neutrophils in CAV, apoptosis and related antigens were investigated in vivo. The 32 patients with CAV were divided into two groups based on their clinical course: (i) non-recurrent (group I; nine cases); and (ii) recurrent (group II; 23 cases). Immunohistopathologically, group I was characterized by stereotypical necrotizing changes of CAV with fibrin exudation of small blood vessels in the upper cutis, and group II was characterized by CAV and fibrous thickening of the vascular walls with significant infiltration of CD3+, UCHL-1+ T cells. Group II was subdivided further: groups IIa (15 cases) and IIb (eight cases); that is, the former was notable for necrotizing changes of CAV, which tended to spread into the proper corium down to the lower cutis; whereas the latter exhibited considerably less marked histological changes of CAV without any spread to the lower cutis. In a comparison of the clinical data among the three groups, there were considerable differences in age, clinical course, localization of purpura and associated disease. In particular, group II showed a high frequency of connective tissue diseases. The presence of apoptosis was seen in a considerable number of neutrophils, and some nuclear debris turned out to be apoptotic bodies by the in situ terminal deoxytransferase (TdT)-catalyzed DNA nick end-labeling (TUNEL) method and electron microscopy. By combining immunohistochemistry with TUNEL, the majority of apoptotic neutrophils and nuclear debris was seen to be ingested by macrophages. In immunohistochemical examinations for apoptosis-related bcl-2 protein and Fas antigen, bcl-2 was recognized only in the cytoplasm of infiltrating T cells, and Fas was positively stained on the cellular membranes of infiltrating T cells and neutrophils in a scattered fashion. Thus, a novel method for neutrophil disposal in CAV was suggested.

Selective induction of interleukin-1 production and tumor killing activity of macrophages through apoptosis by the inhibition of oxidative respiration

Suppression of mitochondrial respiration and increased glycolysis are characteristic features of activated macrophages. We show here that antimycin A, a respiratory inhibitor, induced interleukin-1 synthesis and tumoricidal activity without inducing tumor necrosis factor or nitric oxide. The induction of tumoricidal activity was resistant to inhibitors of tyrosine-specific protein kinases and intracellular glycoprotein transport. The cognate interaction between macrophages and target cells was not a prerequisite for the tumoricidal activity. In contrast, lipopolysaccharide induced the production of interleukin-1, tumor necrosis factor and nitric oxide, the induction of tumoricidal activity being sensitive to genistein and brefeldin A. Antimycin A, like lipopolysaccharide, induced the release of a cytoplasmic enzyme and apoptosis of macrophages. Antimycin A showed anti-metastatic activity in vivo. These results suggest that the inhibition of oxidative respiration would induce apoptosis and the resultant release of soluble effector molecules of macrophages which inhibit tumor metastasis in vivo.

Properties, sequence, and synthesis in Escherichia coli of 1-aminocyclopropane-1-carboxylate deaminase from Hansenula saturnus

The plant hormone ethylene is generated from a unique precursor, 1-aminocyclopropane-1-carboxylate (ACC). In previous studies, ACC deaminase, which degrades ACC to alpha-ketobutyrate and ammonia, was found in four strains of Pseudomonas, characterized, and sequenced. To verify the wider distribution of ACC deaminase in microorganisms, we purified and sequenced ACC deaminase from the yeast Hansenula saturnus. The purified enzyme was active toward ACC, D-serine and dl-coronamic acid, indicating the same stereospecificity as the Pseudomonas enzyme, but unlike the bacterial enzyme it was not active toward beta-chloro-D-alanine and O-acetyl-D-serine. Analyses of peptides from proteolytic digests of the purified and modified ACC deaminase covered more than 90% of its amino acid sequence and showed a blocked N-terminal residue as N-acetylserine. A cDNA encoding the ACC deaminase was isolated from H. saturnus cells incubated in alpha-aminoisobutyrate medium, and sequenced. The yeast enzyme has 441 amino acid residues, of which 60 to 63% are identical to those of reported Pseudomonas enzymes. The open reading frame encoding ACC deaminase was subcloned into pET-11d and expressed in Escherichia coli BL21 (DE3) as an active enzyme.

New diagnostic peritoneal lavage criteria for diagnosis of intestinal injury

BACKGROUND

Although diagnostic peritoneal lavage (DPL) is a well-established, reliably objective method of diagnosis of intraperitoneal injury, it is too sensitive to be used as an indicator for emergency celiotomy. Therefore, since the development of ultrasonography and advanced computed tomographic scanners, the role of DPL has been markedly reduced. Despite such remarkable advances, however, radiologic diagnosis of intestinal injury cannot always provide definitive results, and DPL may still be valuable in such instances. We have developed a new DPL criteria specifically designed to aid in the diagnosis of intestinal injury and have evaluated its effectiveness.

METHODS

From August 1988 to December 1995, we performed DPL in 250 patients with blunt abdominal trauma and analyzed the diagnostic accuracy of our new criteria. We used the standard quantitative white blood cell (WBC) criterion for detection of intestinal injury supplemented by a positive-negative borderline adjusted to WBC > or = red blood cell (RBC)/150, where RBC > or = 10 x 10(4)/mm3.

RESULTS

Our criteria had a diagnostic sensitivity of 96.6% and a specificity of 99.4% for intestinal injury after exclusion of 57 patients in whom DPL was performed within 3 hours or after 18 hours from the time of injury. In 133 patients with hemoperitoneum, emergency celiotomy was performed in only 48; the remaining 85 patients with negative DPL based on the WBC criterion avoided surgery, and conservative management resulted in no complications.

CONCLUSION

With the proposed criteria, DPL can be used to diagnose or exclude intestinal injury even in the presence of hemoperitoneum.

Enzymatic activity and partial purification of solanapyrone synthase: first enzyme catalyzing Diels-Alder reaction

In cell-free extracts of Alternaria solani, an enzymatic activity converting prosolanapyrone II to solanapyrones A and D via oxidation and subsequent Diels-Alder reaction has been found. Chromatography with DEAE-Sepharose provided two active fractions, pools 1 and 2. The former fraction converted prosolanapyrone II to solanapyrones A and D in a ratio of 2.2:1 with optical purities of 99% and 45% ee, respectively. The latter fraction did so in a ratio of 7.6:1 with 99% and nearly 0% ee, respectively. The enzyme partially purified from pool 2 native molecular weight of 40-62 kD and a pl of 4.25. The high reactivity of prosolanapyrone III in aqueous solution and the chromatographic behavior of the enzyme in pool 2 suggest that a single enzyme catalyzes both the oxidation and Diels-Alder reaction.

[A case of pulmonary infection with mycobacterium xenopi]

A 42-year-old man with pulmonary disease caused by Mcobacterium xenopi is described. He had a history of alcohol use of over 20 years. He was admitted to another hospital for evaluation of an abnormal chest shadow. A chest X-ray showed a cavitary shadow with infiltration in the right upper lung field. Acid-fast organisms were recognized in sputum and M. xenopi was identified by DNA-DNA hybridization. Although he had been treated with isoniazid, rifampicin, and ethanbutol for 5 years, sputum remained positive on culture and chest X-ray findings did not improve. He was later admitted to our hospital for surgery, and right upper lobectomy was performed. He has remained well for 18 months since the operation. In Japan, cases of the pulmonary infection with M. xenopi are rare. Surgical resection is required when chemotherapy is unsuccessful.

Giant calcifying epithelioma of Malherbe (pilomatrixoma): imaging features

We present a case of giant calcifying epithelioma of Malherbe (pilomatrixoma) in the right upper arm of a 62-year-old man. It measured 18 x 12 x 8 cm in size, making it the largest of all the cases reported previously. CT clearly demonstrated a well-defined, subcutaneous mass with amorphous calcifications. The mass showed intermediate signal intensity on T2*-weighted MR images and slight contrast uptake on contrast-enhanced MR images. Histopathologically, this tumor showed no aggressive or malignant nature. The patient is without evidence of recurrence or metastasis 3 years following the resection.

CD44 expression on blood eosinophils is a novel marker of bronchial asthma

Bronchial asthma is characterized by infiltration of the respiratory tracts by eosinophils. A wide variety of adhesion molecules expressed by eosinophils have been proposed to be involved in binding of eosinophils to the vascular endothelium and subsequent transmigration from the circulation to the airways, while little is known about CD44 expression on eosinophils. We introduced a novel staining combination with which surface markers on eosinophils could be analyzed without purification prior to staining, and examined the expression of CD44 on eosinophils. Staining of eosinophils with anti-CD 16 and anti-VLA-4 mAbs enabled us to delineate eosinophils as VLA-4high CD 16- cells from any other leukocyte populations in the whole blood. CD44 was found to be constitutively expressed on resting eosinophils, and expression increased upon cytokine-mediated activation. In all bronchial asthma patients examined, CD44high eosinophils were enriched in sputum relative to peripheral blood, indicating that eosinophils in sputum were more activated than those in blood. By comparing the extent of CD44 expression on blood eosinophils from poorly controlled and well-controlled asthma patients, we unexpectedly found that the density of CD44 expression is higher on blood eosinophils from the well-controlled group. Thus, the extent of CD44 expression on blood eosinophils is a novel marker indicative of the mangement of bronchial asthma. Deterioration of the asthma management with a concomitant decrease in CD44 expression on peripheral eosinophils implies that CD44 may play an important role in facilitating the transmigration of activated, CD44high eosinophils from the circulation to the respiratory tracts.

[Responses to customer complaints at commercial laboratories]

For commercial laboratories, one of the routine duties involves responding to various kinds of inquiries and complaints received from customers. As causes of complaints, lack of communication between the laboratory and customer, and test errors were considered. In this paper, complaints received by our laboratory were collected and classified by content, and measures to prevent test error are reported. We think the complaints contain important information that can be used to improve the quality of our laboratory. We hope that reinforcement of communication with customers and promoting test knowledge among the customers can produce more clearly worded complaints which will provide more valuable information. We try to receive and deal with these complaints seriously.

Illegitimate recombination leading to allelic loss and unbalanced translocation in p53-mutated human lymphoblastoid cells

Allelic loss and translocation are critical mutational events in human tumorigenesis. Allelic loss, which is usually identified as loss of heterozygosity (LOH), is frequently observed at tumor suppressor loci in various kinds of human tumors. It is generally thought to result from deletion or mitotic recombination between homologous chromosomes. In this report, we demonstrate that illegitimate (nonhomologous) recombination strongly contributes to the generation of allelic loss in p53-mutated cells. Spontaneous and X-ray-induced LOH mutations at the heterozygous thymidine kinase (tk) gene, which is located on the long arm of chromosome 17, from normal (TK6) and p53-mutated (WTK-1) human lymphoblastoid cells were cytogenetically analyzed by chromosome 17 painting. We observed unbalanced translocations in 53% of LOH mutants spontaneously arising from WTK-1 cells but none spontaneously arising from TK6 cells. We postulate that illegitimate recombination was occurring between nonhomologous chromosomes after DNA replication, leading to allelic loss and unbalanced translocations in p53-mutated WTK-1 cells. X-ray irradiation, which induces DNA double-strand breaks (DSBs), enhanced the generation of unbalanced translocation more efficiently in WTK-1 than in TK6 cells. This observation implicates the wild-type p53 protein in the regulation of homologous recombination and recombinational DNA repair of DSBs and suggests a possible mechanism by which loss of p53 function may cause genomic instability.

Cysteine-S-conjugate beta-lyase activity and pyridoxal phosphate binding site of onion alliin lyase

Purification of onion alliin lyase gave two fractions by cation exchange chromatography. Both fractions showed the comparable high catalytic activity of cysteine-S-conjugate beta-lyase with that of alliin lyase using S-(2-chloro-6-nitrophenyl)-L-cysteine and alliin, S-allyl-L-cysteine sulfoxide as substrates. All the active substrates tested with onion alliin lyase were also active to the cysteine-S-conjugate beta-lyase of Mucor javanicus, but the catalytic activity of the Mucor enzyme was lower for all the substrates. The pyridoxal phosphate binding site of the onion alliin lyase was identified as Lys 285 in the amino acid sequence deduced from cDNA which has been reported. This lysine was conserved in all the sequences from the alliin lyase cDNAs, while similarity was not found between the sequences around pyridoxal phosphate binding sites of both the onion alliin lyase and the Mucor cysteine-S-conjugate beta-lyase.

Cloning and sequencing of a cDNA encoding alpha-glucosidase from sugar beet

A cDNA encoding sugar beet alpha-glucosidase was cloned from a library constructed from mRNA of suspension-cultured cells. The cDNA, 3056 bp in length, had an open reading frame encoding a polypeptide of 913 amino acid residues with a molecular mass of 102,078 Da, included only one of four regions which were conserved in the alpha-amylase family of enzymes. The deduced amino acid sequence from the analysis of the cDNA contained the sequences of the proteolysis peptides and the active site region peptide of sugar beet alpha-glucosidase. The primary structure indicated relatively high homology in the range of 28.2 to 54.3% to those for other alpha-glucosidases. The highest homology was found in barley alpha-glucosidase.

Chlorambucil-induced structural changes in the gpt gene of AS52 cells

The bifunctional alkylating agent chlorambucil (CBC) is a chemotherapeutic agent that induces a high yield of mouse germ-line mutations, apparently due to multi-locus deletions or other chromosomal rearrangements. We investigated the mutagenicity of CBC in cultured mammalian cells by comparing its effect in the AS52/gpt and CHO/hprt gene mutation assays, which detect large and small effects, respectively. CBC significantly increased the mutant frequency in the AS52/gpt assay, but not in the CHO/hprt assay, while the cytotoxic responses to CBC were similar in the two cell lines. This indicates that CBC induced predominantly large deletions or other gross structural changes, and not point or other small mutations. The mutational responses to CBC were similar to the responses to mitomycin C comparing them based on the cytotoxic responses. Molecular analysis of the gpt gene in AS52 mutant cells by electrophoresis following PCR amplification revealed that 81% of CBC-induced mutants lost the entire gpt gene, which is caused by large deletions or interchromosomal recombinations. The loss frequency was lower in spontaneous mutants (42%) and ethylmethanesulfonate-induced mutants (29%). This supports cytogenetic data showing that CBC is a potent clastogen in cultured mammalian cells, inducing predominantly large deletions and/or other gross structural alterations.

Cytotoxic and mutagenic responses to X-rays and chemical mutagens in normal and p53-mutated human lymphoblastoid cells

To investigate the role of p53 as a guardian of the genome, the mutagenic and cytotoxic responses to mutagens were compared for normal (TK6) and p53-mutated (WTK-1) cells. The characteristics of the mutations that occurred in these cells was also examined. Human lymphoblastoid cell lines TK6 and WTK-1 are derived from the same progenitor cell line, but WTK-1 cells have homozygous p53 mutations resulting in overproduction of mutant p53 protein. The spontaneous mutation frequency at the heterozygous thymidine kinase (tk) locus in TK6 and WTK-1 cells was 3.5 X 10(-6) and 101.1 X 10(-6), respectively. WTK-1 cells were more resistant than TK6 cells to cytotoxic damage by X-rays, ethyl methanesulfonate (EMS) and methyl methanesulfonate (MMS), and were more sensitive at the tk locus to the mutagenic effects of X-rays, EMS, MMS and mitomycin C. Molecular analysis of TK mutants by Southern-hybridization demonstrated that 70% of spontaneous mutations and 86% of X-ray induced mutations in TK6 cells resulted from loss of the entire tk allele (loss of heterozygosity; LOH), while 95% of spontaneous and 100% of X-ray induced mutations showed LOH in WTK-1 cells. Densimetric analysis revealed that almost all of the LOH mutants in WTK-1 cells were homozygous at the tk locus, consistent with inter-allelic homologous recombination, or gene conversion. These data indicate that p53-mutated WTK-1 cells are hypermutable, susceptible to some environmental mutagens, and prone to LOH-type gene mutations because of their abnormally high recombinational activity. It may be that genetic instability in p53-mutated cells significantly contribute to the subsequent occurrence of LOH mutations during a multistep tumorigenic process.

Substitutions of alanine for cysteine at a reactive thiol site and for lysine at a pyridoxal phosphate binding site of 1-aminocyclopropane-1-carboxylate deaminase

1-Aminocyclopropane-1-carboxylate (ACC) deaminase catalyzes the cyclopropane ring fragmentation and deamination of ACC. Replacement of cysteine with alanine at a reactive thiol site, Cys-162, of ACC deaminase did not affect the enzyme activity, in spite of the previous result that modification of Cys-162 caused complete loss of the enzyme activity. Substitution of glycine or valine for the cysteine residue gave a higher Km for ACC without a significant change of the K0, indicating that changes of the amino acid side chain had structural effects on substrate binding. Replacement of lysine with alanine at the pyridoxal phosphate (PLP) binding site of the ACC deaminase caused a lower content of PLP and loss of detectable activity of ACC deamination. This mutant enzyme, K51A, showed absorption peaks at 330 nm and 405 nm. The peak at 405 nm was shifted to about 425 nm by the addition of ACC, D-, L-alanine, and D-, L-serine. The formation of aldimine complexes indicated by the spectral shift was reversible. It is suggested that lysine 51 affects the formation of holoenzyme and is important in catalysis.

Eosinophils as a source of matrix metalloproteinase-9 in asthmatic airway inflammation

Bronchial asthma is characterized by eosinophil infiltration and tissue remodeling. Matrix metalloproteinases (MMPs) are thought to play critical roles by degradating interstitial matrices in a wide range of lung diseases associated with reorganization of the airway architecture. To investigate whether MMPs are involved in the pathologic processes of bronchial asthma, we examined MMP expression in asthmatic subjects. In situ hybridization revealed abundant expression of MMP-9 (gelatinase B) mRNA in biopsy specimens from asthmatic subjects (n = 5), with an average positive cell distribution of 117.8 +/- 41.1 (mean +/- SEM)/mm2. In contrast, sparse expression of the mRNA (10.8 +/- 4.8 /mm2) was observed in specimens from normal subjects (n = 4). The vast majority of cells expressing the mRNA were eosinophils in asthmatic tissues (92.2 +/- 1.2%). MMP-9 protein, which was confined to the submucosal cells in the normal subjects, was not abundantly expressed in inflammatory cells, but there was positive reactivity for MMP-9 protein in the extracellular matrix. Immunoelectron microscopic analysis showed sparse immunolocalization of MMP-9 in the perinuclear spaces of eosinophils, but not in the granules. These findings suggest the overexpression of MMP-9 by eosinophils in bronchial tissues of asthmatic individuals, and the participation of MMPs in the pathologic changes in asthmatic airways.