Co-purification of microsomal epoxide hydrolase with the warfarin-sensitive vitamin K1 oxide reductase of the vitamin K cycle

Vitamin K1 oxide reductase activity has been partially purified from rat liver microsomes. A three-step procedure produced a preparation in which warfarin-sensitive vitamin K1 oxide reductase activity was 118-fold enriched over the activity in intact rat liver microsomes. A major component of the multi-protein mixture was identified as a 50 kDa protein that strongly cross-reacts with antiserum prepared against homogeneous rat liver microsomal epoxide hydrolase. The reductase preparation also had a high level or epoxide hydrolase activity against two xenobiotic epoxide substrates. The K(m) values for hydrolysis by the reductase preparation were similar to those for homogeneous microsomal epoxide hydrolase itself, and the specific hydrolase activities of the reductase preparation were 25-35% of the specific activities measured for the homogeneous hydrolase preparation. Antibodies prepared against homogeneous microsomal epoxide hydrolase inhibited up to 80% of reductase activity of the reductase preparation. Homogeneous microsomal epoxide hydrolase had no vitamin K1 oxide reductase activity. This evidence suggests that microsomal epoxide hydrolase, or a protein that is very similar to it, is a major functional component of a multi-protein complex that is responsible for vitamin K1 oxide reduction in rat liver microsomes.

[Clinical and experimental research of Epimedium brevicornum in relieving neuroendocrino-immunological effect inhibited by exogenous glucocorticoid]

OBJECTIVE

To study protective effect of Epimedium brevicornum (EB) on hypothalamus-pituitary-adrenal-thymus (HPAT) axis inhibited by exogenous glucocorticoid.

METHODS

In clinical research, variation of cortisol, adrenocorticotrophin (ACTH), lymphocyte proliferative reaction were observed before and after medication in 65 patients took prednisone, and were randomly divided into Fufang prednisone group (mixture of prednisone and EB) and prednisone group. An experimental model of HPAT axis inhibited by corticosterone (CORT) was established to observe the effect of EB on relevant indices of HPAT axis.

RESULTS

The level of ACTH and CORT in plasma decreased and lymphocyte proliferative reaction reduced in patients (P < 0.05). In experimental study, monoaminic transmitters activated in hypothalamus; weight of pituitary, adrenal and thymus decreased; number of CRH positive neurons in hypothalamic paraventricular nucleus, CRH positive neurofibrilin median eminence and anterior pituitary ACTH positive secretory cells decreased; adrenal fasciculate zone and thymus cortex atrophies; NK cell cytotoxicity and the level of IL-2 and gamma-IFN which were produced by lymphocytes reduced in CORT-rats (P < 0.05). There were significant difference between Fufang prednisone group (clinical research) or EB group (experimental research) and CORT control groups, P < 0.05.

CONCLUSION

EB could relieve neuroendocrino-immunological effect inhibited by exogenous glucocorticoid.

Mechanism-based inactivation of a yeast methylamine oxidase mutant: implications for the functional role of the consensus sequence surrounding topaquinone

The copper-containing yeast methylamine oxidase E406N mutant has an altered consensus sequence surrounding the topaquinone cofactor (residue 405). The mutation has no effect on the final yield of the active-site topaquinone cofactor during biogenesis but causes the enzyme to be inactivated by substrate methylamine [Cai, D., and Klinman, J. P. (1994) Biochemistry 33, 7674-7653]. In this study we show that the inactivation leads to the formation of a covalent adduct, which has a UV/vis spectrum very similar to that of a product Schiff base, an intermediate of topaquinone-catalyzed amine oxidation reactions. The kinetic isotope effects on the second-order rate constant for the inactivation and catalytic turnover are identical, indicating that the two processes share a common intermediate that follows C_H bond cleavage. Resonance Raman spectroscopy provides direct evidence for the accumulation of a neutral product Schiff base species. Removal of excess methylamine leads to recovery of both activity and the native absorption spectrum for E406N, indicating that the cofactor in the inactivated enzyme is chemically competent for hydrolysis. The rate of the reactivation is slow, however; the shortest half-life of the inhibited E406N at 25 degrees C is 5.9 min at pH 6.15. pH effect experiments show that the inactivation and reactivation steps are controlled by a single ionizable group with a pKa of 6.9-7.1; under basic conditions, when this residue is deprotonated, the inactivation is the fastest and the half-life of the inhibited enzyme is the longest. On the basis of the available crystal structures of copper amine oxidases, we propose that a histidine residue in the dimer interface is responsible for the observed ionization. In the wild-type enzyme this histidine is kept protonated by virtue of Glu at position 406. Unlike methylamine, the larger substrates ethylamine and benzylamine give normal turnover with E406N. Disruption of structure at the subunit interface in E406N may allow a rotation of the relatively small topa-product Schiff base complex (formed from methylamine) away from the active-site base to a conformation that is incompetent toward hydrolysis.

Effect of metal on 2,4,5-trihydroxyphenylalanine (topa) quinone biogenesis in the Hansenula polymorpha copper amine oxidase

Previous studies of wild-type and mutant forms of a recombinant copper amine oxidase from Hansenula polymorpha, expressed in Saccharomyces cerevisiae, have indicated a self-processing mechanism for 2,4,5-trihydroxyphenylalanine (topa) quinone biogenesis involving the active site copper (Cai, D., and Klinman, J. P. (1994) J. Biol. Chem. 269, 32039-32042). In contrast to prokaryotic copper amine oxidases, however, it has not been possible to initiate topa quinone formation by the addition of exogenous copper to precursor H. polymorpha amine oxidase lacking copper. Metal analysis of copper-depleted wild-type enzyme reveals 0.2-0.3 mol copper, together with 0.6 mol zinc. Despite changes in the zinc and copper levels in growth media, the level of zinc in purified enzyme remains fairly constant. Further, we have been unable to displace protein-bound zinc by exogenously added copper. The H. polymorpha amine oxidase gene was subsequently expressed in Escherichia coli and found to be almost completely free of copper and zinc. In vitro reconstitution of this apoprotein confirms that zinc binds to H. polymorpha amine oxidase and prevents reconstitution with copper. By contrast, addition of copper first to apoprotein leads to formation of topa quinone and stable activity in the presence of added zinc. These findings indicate efficient binding of either zinc or copper to a site that undergoes little or no exchange. The data confirm that topa quinone biogenesis in the H. polymorpha system is catalyzed by copper and occurs in the absence of added factors. We conclude that the mechanisms of cofactor biogenesis in pro- and eukaryotic systems are likely to be similar or identical. The results described herein imply different pathways for the in vivo assembly of heterologously expressed amine oxidases in S. cerevisiae and E. coli.

Spatiotemporal receptive field organization in the lateral geniculate nucleus of cats and kittens

We have studied the spatiotemporal receptive-field organization of 144 neurons recorded from the dorsal lateral geniculate nucleus (dLGN) of adult cats and kittens at 4 and 8 wk postnatal. Receptive-field profiles were obtained with the use of a reverse correlation technique, in which we compute the cross-correlation between the action potential train of a neuron and a randomized sequence of long bright and dark bar stimuli that are flashed throughout the receptive field. Spatiotemporal receptive-field profiles of LGN neurons generally exhibit a biphasic temporal response, as well as the classical center-surround spatial organization. For nonlagged cells, the first temporal phase of the response dominates, whereas for lagged neurons, the second temporal phase of the response is typically the largest. This temporal phase difference between lagged and nonlagged cells accounts for their divergent behavior in response to flashed stimuli. Most LGN cells exhibit some degree of space-time inseparability, which means that the receptive field cannot simply be viewed as the product of a spatial waveform and a temporal waveform. In these cases, the response of the surround is typically delayed relative to that of the center, and there is some blending of center and surround during the time course of the response. We demonstrate that a simple extension of the traditional difference-of-Gaussians (DOG) model, in which the surround response is delayed relative to that of the center, accounts nicely for these findings. With regard to development, our analysis shows that spatial and temporal aspects of receptive field structure mature with markedly different time courses. After 4 wk postnatal, there is little change in the spatial organization of LGN receptive fields, with the exception of a weak, but significant, trend for the surround to become smaller and stronger with age. In contrast, there are substantial changes in temporal receptive-field structure after 4 wk postnatal. From 4 to 8 wk postnatal, the shape of the temporal response profile changes, becoming more biphasic, but the latency and duration of the response remain unchanged. From 8 wk postnatal to adulthood, the shape of the temporal profile remains approximately constant, but there is a dramatic decline in both the latency and duration of the response. Comparison of our results with recent data from cortical (area 17) simple cells reveals that the temporal development of LGN cells accounts for a substantial portion of the temporal maturation of simple cells.

Crystallographic Study of Yeast Copper Amine Oxidase

The copper-containing amine oxidase from the yeast Hansenula polymorpha (YAO) has been crystallized and partially solved by molecular replacement. It catalyzes the oxidative deamination of primary amines by molecular oxygen to the corresponding aldehydes, ammonia and hydrogen peroxide. It contains a covalently bound redox cofactor, topa quinone, generated by post-translational modification of a single tyrosine side chain. The crystals of YAO are orthorhombic, with space-group symmetry P2(1)2(1)2(1) and unit-cell dimensions a = 138.8, b = 148.2, c = 234.0 A and diffract X-rays beyond 2.0 A resolution. Solution by molecular replacement using the E. coli amine oxidase structure [Parsons, Convery, Wilmot, Yadav, Blakeley, Corner, Philips, McPherson & Knowles (1995). Structure, 3, 1171-1184] as a search model reveals that there are three dimers in the asymmetric unit in a trigonal arrangement having 32 point-group symmetry. The solution agrees well with the self-rotation function of YAO. The non-crystallographic threefold axis lies parallel to a crystallographic twofold screw axis and each dimer has twofold symmetry. Phases from the refined model based on the molecular-replacement solution were used to solve one heavy-atom derivative. Model building from the unbiased isomorphous replacement phases is in progress.

Inhibition of recombinant Ca2+ channels by benzothiazepines and phenylalkylamines: class-specific pharmacology and underlying molecular determinants

To understand the molecular basis of state-dependent pharmacological blockade of voltage-gated Ca2+ channels, we systematically characterized phenylalkylamine and benzothiazepine inhibition of three molecular classes of Ca2+ channels (alpha1C, alpha1A, and alpha1E) expressed from cDNA clones transfected into HEK 293 cells. State-dependent blockade figures importantly in the therapeutically desirable property of use-dependent drug action. Verapamil (a phenylalkylamine) and diltiazem (a benzothiazepine) were imperfectly selective, so differences in the state dependence of inhibition could be compared among the various channels. We found only quantitative differences in pharmacological profile of verapamil: half-maximal inhibitory concentrations spanned a 2-fold range (70 microM for alpha1A, 100 microM for alpha1E, and 110 microM for alpha1C), and inhibition was state dependent in all channels. In contrast, diltiazem produced only state-dependent block of alpha1C channels; alpha1A and alpha1E channels demonstrated state-independent block despite similar half-maximal inhibitory concentrations (60 microM for alpha1C, 220 microM for alpha1E, and 270 microM for alpha1A). To explore the molecular basis for the sharp distinction in state-dependent inhibition by diltiazem, we constructed chimeric channels from alpha1C and alpha1A and localized the structural determinants for state dependence to repeats III and IV of alpha1C, which have been found to contain the structures required for benzothiazepine binding. We then constructed a mutant alpha1C construct by changing three amino acids in IVS6 (Y14901, A1494S, 11497M) that have been implicated as key coordinating sites for avid benzothiazepine binding. Although these mutations increased the half-maximal inhibitory concentration of diltiazem inhibition by approximately 10-fold, the state-dependent nature of inhibition was spared. This result points to the existence of physically distinct elements controlling drug binding and access to the binding site, thereby favoring a "guarded-receptor" rather than a "modulated-receptor" mechanism of drug inhibition.

Isometric muscle strength of Chinese young males in Taiwan

This paper represents the results of an anthropometric measurement of the isometric muscle strength of Chinese young males in Taiwan aged from 16 to 20 years. The study uses a sample of 120 male students and measures four types of muscle strength: (1) right arm strength in exerting pull, push, adduction, abduction, lift, and press directions with five elbow angles (60, 90, 120, 150 and 180 degrees) in seated posture; (2) grip strength of both hands; (3) backlift strength: and (4) chest expanding strength. The obtained data are analysed and listed. Comparisons are made between the results of this study and those from domestic and foreign studies available in the literature. In general, their pattern is similar, but values obtained in this study are relatively smaller than those obtained in western countries.

[Changes of inflammatory mediator in aucte necrotizing pancreatitis and effect of somatostatin analogne stilamin in rats]

OBJECTIVES

To investigate the changes of inflammatory mediator in ANP and to explore the effectiveness of stilamin treatment on ANP.

METHODS

SD rats were divided into experimental groups (ANP = 12, ANP + NS = 10, ANP + Stilamin = 12) and control group (NC = 10). Rat ANP models were made by retrograde injection of 3.5% sodium taurocholate 2.5 ml/kg into the pancreatic duct, and treated by intravenous injection of stilamin 84 micrograms.kg-1.d-1 or same amount of normal saline respectively. Serum IL-1 beta, IL-6, IL-12, TNF-alpha, PLA2, amylase and endotoxin were examined. Finally, the morphology and pathology of the pancreas, liver, lung, heart and kidney, as well as the electronmicroscopical investigation of liver and lung cells were observed.

RESULTS

The mean IL-1 beta, IL-6, IL-12, TNF-alpha, in the ANP and ANP + NS group were higher than those in the ANP + stilamin group and Control group (P < 0.01). The endotoxin, amlyase, PLA2 level in the ANP + stilamin group was lower than those in the ANP and ANP + NS groups (P < 0.001). ANP significantly increased white blood cell chemotax and infiltration, as well as hemorrhagic focus in liver, kidney and lung, but the pathological examinations of the liver, pancreas, lung and kidney demonstrated much less destruction in the stilamin group.

CONCLUSIONS

Inflammatory cytokins play an essential role to induce pathophysiological process of ANP, and its related MODS may be effectively prevented and treated by stilamin.

[The actions of nucleating proteins in vesicle aggregation and fusion: a preliminary study]

After investigation of the effects of Con A-binding proteins, the major biliary pronucleating effectors system on the figures and lipid composition of model biliary vesicles, the authors found that Con A-binding proteins accelerate aggregation and fusion of vesicles as a result of increased vesicular cholesterol and decreased vesicular phospholipids as well as cholesterol-saturated vesicles. We also found that vesicular proteins though in small quantity are potent in pronucleating effects. The distribution of several known nucleating proteins between the vesicles and micelles is quite different, and there are higher content and more potent pronucleating effectors in patients with cholesterol gallstone than those with pigment stone. By affinity staining method, con A-binding proteins were shown in native biliary vesicles as lipid-protein complex. These results suggest that the existence and changes in their quantity and quality of vesicular nucleating proteins play an important role in vesicle aggregation and fusion.

Generation of multiple mRNA fingerprints using fluorescence-based differential display and an automated DNA sequencer

Differential display is a method for the survey, analysis and comparison of gene expression in eukaryotic cells and tissues. Differential display involves isolation of high-quality nondegraded RNA, selective reverse transcription of polyadenylated mRNA using specific anchored oligopolydeoxythymidine [oligo(dT)] primers, and the subsequent PCR amplification of the cDNA with the same oligo(dT), an arbitrary upstream primer and radioisotopes for labeling the PCR products. The radioisotopically labeled products are then separated on a sequencing gel. In this report, we describe a rapid, specific, nonradioactive fluorescent differential display methodology in which fluorescently differentially labeled anchored oligo(dT) downstream primers are used in the reaction, with subsequent analysis of fluorescently labeled PCR products on an automated sequencer. Complete gene expression profiles, containing multiple mRNA fingerprints are possible by the simultaneous comparison of the multicolored banding patterns of the fluorescently differentially labeled products from several primer combinations. This modification of the differential display technique simplifies the assay and increases the throughput of high sample volumes required for comparative gene expression studies in various clinical applications.

Positional cloning of a gene for nematode resistance in sugar beet

The Hs1(pro-1) locus confers resistance to the beet cyst nematode (Heterodera schachtii Schmidt), a major pest in the cultivation of sugar beet (Beta vulgaris L.). The Hs1(pro-1) gene was cloned with the use of genome-specific satellite markers and chromosomal break-point analysis. Expression of the corresponding complementary DNA in a susceptible sugar beet conferred resistance to infection with the beet cyst nematode. The native Hs1(pro-1) gene, expressed in roots, encodes a 282-amino acid protein with imperfect leucine-rich repeats and a putative membrane-spanning segment, features similar to those of disease resistance genes previously cloned from higher plants.

Retrovirus-mediated wild-type p53 gene transfer to tumors of patients with lung cancer

A retroviral vector containing the wild-type p53 gene under control of a beta-actin promoter was produced to mediate transfer of wild-type p53 into human non-small cell lung cancers by direct injection. Nine patients whose conventional treatments failed were entered into the study. No clinically significant vector-related toxic effects were noted up to five months after treatment. In situ hybridization and DNA polymerase chain reaction showed vector-p53 sequences in posttreatment biopsies. Apoptosis (programmed cell death) was more frequent in posttreatment biopsies than in pretreatment biopsies. Tumor regression was noted in three patients, and tumor growth stabilized in three other patients.

Long-term oral administration of L-arginine enhances endothelium-dependent vasorelaxation and inhibits neointimal thickening after endothelial denudation in rats

OBJECTIVE

To further prove the hypothesis that local decrease of nitric oxide (NO) synthesis and/or its activity might be critically important in the disturbance of vascular homeostasis after vascular injuries.

METHODS

Intimal thickening model induced by air-drying denudation of rat right common carotid artery was performed to evaluate the effects of long-term oral administration of L-arginine on neointimal thickening and acetylcholine-induced endothelium-dependent vasorelaxation (EDR) by histomorphometric and functional studies.

RESULTS

Reductions in EDR function persisted and simultaneously developed prominent neointimal thickening by 14 days after denudation. Long-term oral supplementation of L-arginine (1 g/kg/day) significantly enhanced EDR from 43.5% +/- 12.35% to 68.8% +/- 9.0% (n = 10, P < 0.001) and reduced neointimal thickening from 62.45 microns +/- 11.26 microns to 21.45 microns +/- 6.34 microns (n = 10, P < 0.001) as compared with each control animals.

CONCLUSIONS

This study shows that oral administration of L-arginine significantly inhibits neointimal thickening and preserves NO-mediated EDR in experimental endothelial denudation, suggesting an important role for L-arginine, NO pathway in the regulation of vascular homeostasis after endothelial injury which might be salutary in prevention restenosis after coronary angioplasty.

[Esophagogastrostomy covered by sero-muscular flap of gastric wall in the treatment of gastric cardia cancer in 100 cases]

A new operative procedure-esophagogastrostmy covered by sero-muscular flap of gastric wall to treat cancer of gastric cardia was designed by the authors in order to prevent anastomotic complications. One hundred cases with cases of gastric cardiac 97 cases with adenocarcinoma and 3 cases with squamous cell carcinoma of esophago-cardiac iunction were treated with the new anastomotic method without operative mortality and anastomotic complicatins within one year after surgery.

[Changes in cytosolic free calcium and thromboxane B2 synthesis in platelets from diabetic subjects]

Using fura-2, a fluorescence indicator, we evaluated the changes of platelet cytosolic free calcium concentration ([Ca2+]i) and its role in regulation of thromboxane B2 (TXB2) synthesis in patients with diabetes mellitus (DM group, n = 27) and in healthy subjects (control group, n = 15). The A23187-evoked elevation of [Ca2+]i and TXB2 production were higher in the DM group than in the control group (P < 0.01 respectively). The rise in [Ca2+]i was correlated positively with TXB2 production. In contrast, stimulation with arachidonic acid, TXB2 production was unaltered between the groups, although arachidonate-induced [Ca2+]i was higher in the DM group than in the control group (P < 0.05). The results suggested that changes in platelets [Ca2+]i in diabetic subjects may contribute to increase in TXB2 synthesis, involved libration of free arachidonate from membrance phospholipids by the action of phospholipases. Since no significant difference was found between the diabetic patients with microangiopathy (n = 13) and without microangiopathy (n = 14), the results above may be involved in the development of diabetic microangiopathy.

Physical mapping and cloning of a translocation in sugar beet (Beta vulgaris L) carrying a gene for nematode (Heterodera schachtii) resistance from B. procumbens

Two diploid (2n=18) sugar beet (Beta vulgaris L.) lines which carry monogenic traits for nematode (Heterodera schachtii Schm.) resistance located on translocations from the wild beet species Beta procumbens were investigated. Short interspersed repetitive DNA elements exclusively hybridizing with wild beet DNA were found to be dispersed around the translocations. The banding pattern as revealed by genomic Southern hybridization was highly conserved among translocation lines of different origins indicating that the translocations are not affected by recombination events with sugar beet chromosomes. Physical mapping revealed that the entire translocation is represented by a single Sal I fragment 300 kb in size. A representative YAC (yeast artifical chromosome) library consisting of approximately 13,000 recombinant clones (2.2 genome equivalents) with insert sizes ranging between 50 and 450 kb and an average of 130kb has been constructed from the resistant line A906001. Three recombinant YACs were isolated from this library using the wild beet-specific repetitive elements as probes for screening. Colinearity between YAC inserts and donor DNA was confirmed by DNA fingerprinting utilizing these repetitive probes. The YACs were arranged into two contigs with a total size of 215 kb; these represent a minimum of 72% of the translocation.

[Surgical treatment of benign stenosis of the esophagus]

From Nov. 1972 to 1983 Oct., 88 patients with benign stenosis of the esophagus were operated on. The youngest patients was 18 months, and the oldest 63 years. From corrosive injury of esophagus to operation, the shortest period was 13 days and longest 10 years (mean 120 days). In 85 patients, transverse colon was used to replace the esophagus substernally. In 2 patients, reconstruction was done by gastric tube. One patient used transverse colon and part of descending colon. Preoperative gastrostomy was made in 5 patients. There was no operative mortality. One patient developed anastomotic stenosis postoperatively. He refused reoperation and died. The remaining patients survived with a normal life. For the reconstruction of esophagus, problems such as choice of grafts, time of operation, resection of scar or not, and place of anastomosis were discussed.

Contrast coding by cells in the cat's striate cortex: monocular vs. binocular detection

Many psychophysical studies of various visual tasks show that performance is generally better for binocular than for monocular observation. To investigate the physiological basis of this binocular advantage, we have recorded, under monocular and binocular stimulation, contrast response functions for single cells in the striate cortex of anesthetized and paralyzed cats. We applied receiver operating characteristic analysis to our data to obtain monocular and binocular neurometric functions for each cell. A contrast threshold and a slope were extracted from each neurometric function and were compared for monocular and binocular stimulation. We found that contrast thresholds and slopes varied from cell to cell but, in general, binocular contrast thresholds were lower, and binocular slopes were steeper, than their monocular counterparts. The binocular advantage ratio, the ratio of monocular to binocular thresholds for individual cells, was, on average, slightly higher than the typical ratios reported in human psychophysics. No single rule appeared to account for the various degrees of binocular summation seen in individual cells. We also found that the proportion of cells likely to contribute to contrast detection increased with stimulus contrast. Less contrast was required under binocular than under monocular stimulation to obtain the same proportion of cells that contribute to contrast detection. Based on these results, we suggest that behavioral contrast detection is carried out by a small proportion of cells that are relatively sensitive to near-threshold contrasts. Contrast sensitivity functions (CSFs) for the cell population, estimated from this hypothesis, agree well with behavioral data in both the shape of the CSF and the ratio of binocular to monocular sensitivities. We conclude that binocular summation in behavioral contrast detection may be attributed to the binocular superiority in contrast sensitivity of a small proportion of cells which are responsible for threshold contrast detection.

The thylakoid translocation of subunit 3 of photosystem I, the psaF gene product, depends on a bipartite transit peptide and proceeds along an azide-sensitive pathway

Subunit 3 of photosystem I (PSI-3), the product of the nuclear psaF gene, is the docking protein for plastocyanin during photosynthetic electron transport in thylakoid membranes and is synthesized in the cytosol with a transit peptide that resembles structurally the bipartite targeting signals of hydrophilic, lumenal components such as plastocyanin. In organello import experiments performed with the authentic PSI-3 precursor and chimeric polypeptides consisting of residue-correct fusions of transit peptides and mature proteins derived from different plastid proteins demonstrate that the PSI-3 transit peptide is indeed capable of translocating proteins into the thylakoid lumen and that, conversely, mature PSI-3 depends on a bipartite transit peptide for its thylakoid transfer. Of the three recently described translocation/integration pathways for nucleus-encoded proteins carrying bipartite transit peptides that are distinct in their physiological requirements and strictly protein-specific, PSI-3, like plastocyanin and the 33-kDa protein of the oxygen-evolving complex, is translocated by a pathway that involves stromal factors but no proton gradient across the membrane. It is not affected by saturating amounts of the precursor for the 23-kDa protein of the oxygen-evolving complex that follows the latter route. Thylakoid translocation of PSI-3 is, however, impaired in the presence of sodium azide, which indicates that a homolog to the bacterial SecA protein might be involved in this process suggesting, thus, a prokaryote-like translocation pathway. The azide-sensitive factor appears to interact predominantly with the transit peptide of a precursor protein, since chimeras consisting of a presequence from an azide-resistant precursor and a mature part of an azide-sensitive polypeptide are still translocated in the presence of the inhibitor.

Evidence of a self-catalytic mechanism of 2,4,5-trihydroxyphenylalanine quinone biogenesis in yeast copper amine oxidase

Copper amine oxidases are representative of a new class of redox enzymes that contain a peptide-bound quinone cofactor, generated by posttranslational modification of amino acid side chain(s). We have investigated the mechanism for the biogenesis of 2,4,5-trihydroxyphenylalanine quinone (TPQ) in amine oxidase with two site-specific mutants of the yeast methylamine oxidase. Our results show that the capacity for TPQ formation in vivo is abolished when a putative ligand to copper, His-456, is changed to Asp; this H456D mutant binds copper at a low level (approximately 4.1%), relative to the wild-type protein. In contrast, altering the active site consensus sequence that contains the precursor tyrosine does not affect TPQ production. The data implicate a self-catalysis mechanism for TPQ biogenesis, in which the protein-bound copper plays a key role. We propose that the minimal information required for TPQ biogenesis lies in a structural motif consisting of the copper site and the precursor tyrosine.

Copper amine oxidase: heterologous expression, purification, and characterization of an active enzyme in Saccharomyces cerevisiae

A copper amine oxidase gene from a methylotrophic yeast Hansenula polymorpha has been expressed in Saccharomyces cerevisiae under the control of the ADHI promoter and the recombinant protein purified to near homogeneity. The recombinant enzyme is as active as the native enzyme in catalyzing methylamine oxidation. We demonstrate that it is a quinoprotein by redox-cycling staining and titrations with carbonyl reagents. The absorption spectral properties of the recombinant amine oxidase and its phenylhydrazine derivative are very similar to those of other copper amine oxidases. The cofactor in the enzyme is 2,4,5-trihydroxyphenylalanine (topa) quinone, as demonstrated by the pH-dependent shift in the lambda max of the p-nitrophenylhydrazone adduct. Alignment of an active-site peptide and DNA-derived protein sequences reveals a tyrosine residue as the precursor to topa quinone, consistent with findings with other copper amine oxidases. All evidence presented herein indicates that the heterologously expressed copper amine oxidase protein is processed posttranslationally in S. cerevisiae to form an active enzyme with an intact cofactor. This occurs despite an inability of S. cerevisiae to utilize amines as a nitrogen source. The implications of this study for the mechanism of topa quinone biogenesis are discussed.

Primary structures for a mammalian cellular and serum copper amine oxidase

The 6-hydroxydopa quinone-containing active site peptide from bovine serum amine oxidase has been found to be highly homologous to a segment of a cloned human kidney amiloride-binding protein (Barbry, P., Champe, M., Chassande, O., Munemitsu, S., Champigny, G., Lingueglia, E., Maes, P., Frelin, C., Tartar, A., Ullrich, A., and Lazdunski, M. (1990) Proc. Natl. Acad. Sci. U.S.A. 87, 7347-7351). Additionally, a second 38-residue tryptic peptide (peptide XI) isolated from bovine serum amine oxidase shows 82% identity with a portion near the carboxyl terminus of the human kidney amiloride-binding protein. When an extended active site peptide was isolated from porcine kidney diamine oxidase (Janes, S. M., Palcic, M. M., Scaman, C. H., Smith, A. J., Brown, D. E., Dooley, D. M., Mure, M., and Klinman, J. P. (1992) Biochemistry 31, 12147-12154), it was found to be fully contained in the human kidney amiloride-binding protein. Examination of amiloride binding to bovine serum amine oxidase and porcine kidney diamine oxidase reveals dissociation constants of 196 and 9.1 microM, respectively. Taken together, these findings indicate that the cDNA isolated for human kidney amiloride-binding protein encodes a human kidney diamine oxidase. Two oligonucleotides, based on the tryptic peptide XI and active-site peptide of bovine serum amine oxidase, were used to amplify a portion of cDNA from a commercial bovine liver cDNA library through the use of the polymerase chain reaction. A full-length clone (2.7 kilobase pairs) for bovine serum amine oxidase was subsequently obtained through screening of the same cDNA library with the amplified 0.7-kilobase pair cDNA. These studies provide the first primary sequences for a mammalian cellular and serum copper amine oxidase. Computer alignment of amine oxidase cDNA-derived protein sequences reveals three conserved histidine residues, which are likely to be ligands to copper.

Effects of gap junction conductance on dynamics of sinoatrial node cells: two-cell and large-scale network models

A computational model of single rabbit sinoatrial (SA) node cells has been revised to fit data on regional variation of rabbit SA node cell oscillation properties. The revised model simulates differences in oscillation frequency, maximum diastolic potential, overshoot potential, and peak upstroke velocity observed in cells from different regions of the node. Dynamic properties of electrically coupled cells, each with different intrinsic oscillation frequency, are studied as a function of coupling conductance. Simulation results demonstrate at least four distinct regimes of behavior as coupling conductance is varied: a) independent oscillation (Gc < 1 pS); b) complex oscillation (1 < or = Gc < 220 pS); c) frequency, but not waveform entrainment (Gc > or = 220 pS); and d) frequency and waveform entrainment (Gc > or = 50 nS). The conductance of single cardiac myocyte gap junction channels is about 50 pS. These simulations therefore show that very few gap junction channels between each cell are required for frequency entrainment. Analyses of large-scale SA node network models implemented on the Connection Machine CM-200 supercomputer indicate that frequency entrainment of large networks is also supported by a small number of gap junction channels between neighboring cells.

The presequence of a chimeric construct dictates which of two mechanisms are utilized for translocation across the thylakoid membrane: evidence for the existence of two distinct translocation systems

The translocation of plastocyanin across the thylakoid membrane in Pisum sativum has been studied in reconstitution assays and using chimeric constructs. The reconstitution assays demonstrate that plastocyanin translocation is absolutely dependent on the presence of a stromal factor(s) and nucleotide triphosphates (NTPs), whereas neither element is required for the translocation of the 23 or 16 kDa proteins of the oxygen-evolving complex. Previous studies had revealed that the transthylakoidal delta pH is essential for translocation of the 23 and 16 kDa proteins but unnecessary for plastocyanin translocation. The basis for these mechanistic differences has been tested by analysing the translocation of a chimeric construct consisting of the presequence of the 23 kDa protein linked to the mature plastocyanin sequence. This construct is efficiently imported into thylakoids in the absence of stromal extracts or NTPs and translocation across the thylakoid membrane within intact chloroplasts is totally inhibited by the uncoupler nigericin: the translocation requirements are thus identical to those of the pre-23 kDa protein and diametrically opposite to those of pre-plastocyanin. Transport across the thylakoid membrane of a second fusion protein, consisting of the presequence of the 16 kDa protein linked to mature plastocyanin, is also dependent on a delta pH. The data suggest that two distinct systems are involved in the translocation of proteins across the thylakoid membrane, with each system recognizing specific signals within the presequences of a subset of lumenal protein precursors.

Lignin-degrading peroxidases of Phanerochaete chrysosporium

Lignin and manganese peroxidases are secreted by the basidiomycete Phanerochaete chrysosporium during secondary metabolism. These enzymes play major roles in lignin degradation. The active site amino acid sequence of these lignin-degrading peroxidases is similar to that of horseradish peroxidase (HRP) and cytochrome c peroxidase (CcP). The mechanism by which they oxidize substrates also appears to be the similar. pH has a similar effect on lignin peroxidase compound I formation as on HRP or CcP; however, the pKa controlling compound I formation for lignin peroxidase appears to be much lower. Lignin-degrading peroxidases are able to catalyze the oxidation of substrates with high redox potential. This unique ability is consistent with a heme active site of low electron density, which is indicated by high redox potential.

Doppler flowmeter-assessed circadian rhythms in neonatal cardiac function, family history, and intrauterine growth retardation

This study examines the circadian variation of aortic blood flow velocity, acceleration, and distance of stroke, assessed every 4 hours for 24 hours by Doppler ultrasound in 88 human newborns. Groups 1 and 2 involve neonates with a negative family history of high blood pressure or myocardial infarction monitored during the first day or between the second and tenth days postpartum, respectively; groups 3 to 6 are 2- to 10-day-old babies with a positive family history of high blood pressure (group 3) or of myocardial infarction (group 4) or with a negative family history and intrauterine growth retardation (group 5) or born prematurely (group 6). Cosinor analyses demonstrate a circadian rhythm for all variables in groups 2 and 5 (p < 0.001), with overall high values occurring around 17:40. In group 2, a circadian rhythm remains demonstrable in boys and girls considered separately, and mostly so in arbitrary subgroups of different sizes, with only slight differences in rhythm parameters among them. These results show that, with relatively small samples, reproducible circadian rhythms of cardiac function can be detected shortly after birth in neonates with a negative family history of high blood pressure or myocardial infarction.