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Biomedical subjects

A Ohta

Publications and source records attributed to A Ohta.

At least 289 records · Page 16Linked to original sources
PubMed1985

Biosynthesis of novel acidic phospholipid analogs in Escherichia coli.

When cultured in the presence of 600 mM D-mannitol, Escherichia coli K-12 cells synthesized two novel phospholipids. The identities of these compounds are postulated to be phosphatidylmannitol and diphosphatidylmannitol, the sugar alcohol analogs of phosphatidylglycerol and cardiolipin, respectively. The nonacylated glycerol moieties of the normal acidic phospholipids were substituted by D-mannitol. The formation of the analogs was significantly enhanced when strains harboring the pss-1 allele, a temperature-sensitive mutation in phosphatidylserine synthase (Ohta and Shibuya, J. Bacteriol. 132:434-443, 1977), were grown at 42 degrees C, and the accumulation of the analogs was maximum in late stationary phase; more than 90% of the total cellular lipids were these novel phospholipids. Strains with a defective cardiolipin synthase (Pluschke et al., J. Biol. Chem. 253:5048-5055, 1978) failed to form the analog lipids, whereas cells with increased cardiolipin synthase activity due to the presence of a pBR322-derived recombinant plasmid containing the structural gene for cardiolipin synthase produced more mannitol lipids than wild-type strains. These observations and the structures of the analog lipids indicated that cardiolipin synthase participates in the formation of these novel phospholipids. We suggest that reversible alcoholysis and condensation, in addition to low substrate specificity of the enzyme, are the mechanisms involved in this process. Addition to the medium of other straight-chain alditols, D-arabitol, ribitol, xylitol, erythritol, and L-threitol also yielded pairs of novel phospholipids, whereas sorbitol or galactitol produced only one analog in small quantities. These acidic phospholipid analogs have not been reported in any living system. They should be useful in the study of structure-function relationships of phospholipids and in manipulating the structures of various membrane systems.

Escherichia coli↗
PubMed1985

Alteration of phospholipid composition by combined defects in phosphatidylserine and cardiolipin synthases and physiological consequences in Escherichia coli.

Escherichia coli K-12 derivatives with a common genetic background carrying, either alone or in combination, the pss-1 allele coding for a temperature-sensitive phosphatidylserine synthase (A. Ohta and I. Shibuya, J. Bacteriol. 132:434-443, 1977) and cls- for a defective cardiolipin synthase (G. Pluschke et al., J. Biol. Chem. 253:5048-5055, 1978) were constructed. The phospholipid polar headgroup compositions of these strains were significantly different from each other depending on their genotypes and growth temperature, whereas other membrane characteristics such as the total phospholipid content, fatty acid composition, membrane protein profile, and lipopolysaccharide content were practically the same, suggesting that the phenotypes of these strains were the direct consequences of abnormalities in membrane phospholipid composition. The cls pss-1 double mutation caused an unusual accumulation of phosphatidylglycerol with an extremely low content of cardiolipin. The cls mutation alone was found to give a growth defect, and its introduction into a pss-1 mutant resulted in an enhanced temperature sensitivity of growth. Addition to a broth medium of a proper concentration of sucrose, NaCl, Mg2+, or Ca2+ allowed the growth of a pss-1 mutant at otherwise nonpermissive temperature, but a pss-1 cls double mutant required the combined addition of sucrose or NaCl and MgCl2 for full growth at 42 degrees C. The possible mechanisms for these physiological consequences of the mutations are discussed on a molecular basis. The remedial effects of culture supplements allowed the pss-1 mutants to grow at 42 degrees C resulting in enhanced abnormalities of membrane phospholipid composition.

CDPdiacylglycerol-Serine O-Phosphatidyltransferase↗
PubMed1985

Molecular cloning of the cls gene responsible for cardiolipin synthesis in Escherichia coli and phenotypic consequences of its amplification.

The cls gene responsible for cardiolipin synthesis in Escherichia coli K-12 was cloned in a 5-kilobase-pair DNA fragment inserted in a mini-F vector, pML31, and then subcloned into a 2.0-kilobase-pair fragment inserted in pBR322. The initial selection of the gene was accomplished in a cls pss-1 double mutant that had lesions in both cardiolipin and phosphatidylserine synthases and required either the cls or the pss gene product for normal growth at 42 degrees C in a broth medium, NBY, supplemented with 200 mM sucrose. The cloned gene was identified as the cls gene by the recovery and amplification of both cardiolipin and cardiolipin synthase in a cls mutant as well as by the integration of a pBR322 derivative into its genetic locus at 27 min on the chromosome of a polA1 mutant. The maxicell analysis indicated that a protein of molecular weight 46,000 is the gene product. The cls gene is thus most likely the structural gene coding for cardiolipin synthase. Hybrid plasmids of high copy numbers containing the cls gene were growth inhibitory to pss-I mutants under the above selective conditions, whereas they inhibited neither the growth of pss-I mutants at 30 degrees C nor that of pss+ strains at any temperature. Amplification of cardiolipin synthase activity was observed, but was not proportional to the probable gene dosage (the enzyme activity was at most 10 times that in wild-type cells), and cardiolipin synthesis in vivo was at the maximum 1.5 times that in wild-type strains, implying the presence in E. coli cells of a mechanism that avoids cardiolipin overproduction, which is possibly disadvantageous to proper membrane functions.

Cardiolipins↗
PubMed1985

Effects of nicardipine on ischemic mechanical failure and tissue injury in isolated perfused rat heart.

Using a Langendorff rat heart preparation, we examined effects of nicardipine, a calcium channel blocker, on different stages of ischemic damage, characterized by a development of contracture and leakage of intracellular enzymes. Maximum recoveries of heart rate (HR) and peak left ventricular pressure-HR product after 20 min ischemia were attenuated by about 25% compared with those before ischemia. When nicardipine (0.1 mumol) was added to the perfusate 5 min prior to ischemia, this mechanical failure recovered completely to the pre-ischemic level. Although a significant increase in left ventricular end-diastolic pressure was observed in hearts exposed to 30 min ischemia, the amount of creatine kinase (CK) released during re-flow after 30 min ischemia was not enhanced by contracture but was proportional to the duration of ischemia (compared with that of 20 min ischemia). Nicardipine reduced CK leakage by 25% after 30 min ischemia but did not alter either ATP levels or coronary flow. The beneficial effects of nicardipine on ischemic damage are probably related to inhibition of calcium influx (Terai et al: Biochem Pharmacol 30: 375, 1981), which may accompany reperfusion of ischemic myocardium.

Adenine Nucleotides↗
PubMed1984

[Experimental multiple primary malignant tumors induced by chemical carcinogen].

Experimental induction of multiple primary malignant tumors has been observed in laboratory animals exposed to various carcinogens or irradiation. The development of the tumor by chemical carcinogens is usually multiple. In order to explain different susceptibilities of animals to carcinogenic effect of chemicals, several factors such as different genetic background, aging, dose of drugs and so on have to be taken into consideration. The tumorigenicity of DMBA, MNNG, and 3'-Me-DAB was studied in five strain rats, that is Wistar, Sprague-Dawley, inbred Fischer, inbred Lewis, and inbred Brown-Norway rats. The relationship between multiple tumor, dose of carcinogen, age of animals, and species (strain) of animals is discussed.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1984

[Prognostic significance of the initial clinical findings in patients over 40 years of age with secundum atrial septal defect].

Controversy concerning medical versus surgical management of elderly patients with secundum atrial septal defect (ASD II) remains unsolved. To clarify this problem, we studied relation between initial clinical findings and long-term prognosis of patients with isolated ASD II over 40 years of age. Of 47 patients medically managed, 13 patients died during the follow-up period. Among these, 11 died of congestive heart failure (CHF), and 2 died of non-cardiac disease. Mean age and follow-up period of these 11 were 68.1 +/- 9.0 and 6.7 +/- 5.1 years, respectively, and those of 34 survivors were 61.9 +/- 7.5 and 7.7 +/- 5.8 years, respectively. All 6 patients of functional capacity III-IV (NYHA classification), and 5 of NYHA II, died. Seven patients of NYHA II progressed to NYHA III-IV, and the other 20 of NYHA II and all 7 patients of NYHA I remained unchanged during the follow-up. Overt CHF (p less than 0.001), mitral and/or tricuspid regurgitation (p less than 0.01), combination with arterial hypertension and/or ischemic heart disease (p less than 0.05), atrial fibrillation (p less than 0.01), P-sinistrocardiale (p less than 0.001), and R/S (V6) less than 2.0 (p less than 0.01), cardiothoracic ratio greater than 55% (p less than 0.001), width of right descending branch of the pulmonary artery greater than 25 mm (p less than 0.01), and mitral valve prolapse in the echocardiogram (p less than 0.05) were significantly frequent in the cases clinical deterioration. Of 32 patients, whose functional capacities were NYHA II initially, 12 showed progression and 20 were unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1984

[Computerized processing of two-dimensional echo-cardiograms: its application for quantitating left ventricular regional contractility and three-dimensional echocardiography].

This study assessed the computerized processing of two-dimensional echocardiograms for quantitating left ventricular regional contractility and for computer reconstruction of the left ventricle; so-called three-dimensional echocardiography. Computer analysis of two-dimensional echocardiograms for quantitative evaluations of the left ventricular regional contractility in myocardial infarction: A new practical method for computer digital image processing of two-dimensional echocardiograms was developed for quantitating left ventricular regional contractility. Short-axis cross-sectional images of the left ventricle at the levels of the mitral valve (MV), papillary muscles (PM) and the apex (AP) were recorded using a phased array sector scanner in thirty patients with healed myocardial infarction and fifteen normal control subjects. The echocardiographic data were recorded on the video tape and transferred to a minicomputer via interface circuits, digitized, and processed automatically. Each digitized image consisted of 256 X 256 pixels with a gray scale of 256 values. The edges of the endocardial and epicardial walls were detected by applying sequential steps including smoothing, dynamic thresholding, region growing, and filling of small holes. The rationale of edge detection depended on assuming that abrupt changes in gray levels occurred at the boundary, and that the points with maximum gradient values were boundaries of the left ventricular wall. Best-fit contours of endocardial and epicardial edges were drawn by fitting a spline. Besides this automatic edge tracing, endocardial and epicardial edges were also manually traced using a digi-pen system, whose results coincided well with automatic tracings. After detection of edges of endocardial and epicardial walls, the short-axis cross sectional left ventricular wall at each level was divided into eight segments. The geometric center of the end-diastolic left ventricular cavity and the axis connecting this with the posterior end of the right side of the septum was used as the reference point and line (fixed reference system). End-diastolic and end-systolic segmental hemiaxes, segmental area, segmental wall thickness and changes during the cardiac cycle were measured and calculated automatically in each segment using a computer. Regional contractility of the left ventricle was evaluated by percent systolic changes of the segmental hemiaxis, area and wall thickness. These values were significantly reduced in the infarcted left ventricular wall as defined by left ventriculography and coronary angiography.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1983

Inhibition by quinacrine of depolarization-induced acetylcholine release and calcium influx in rat brain cortical synaptosomes.

The effects of quinacrine on depolarization-induced [3H]acetylcholine (ACh) release and 45Ca2+ influx were examined in rat brain cortical synaptosomes. Quinacrine significantly reduced the stimulated release of [3H]ACh by high K+ and veratridine without affecting the spontaneous efflux from the preloaded synaptosomes. Quinacrine had no effect on ionophore A23187-induced release of [3H]ACh from the synaptosomes. Quinacrine (100 microM) markedly diminished the stimulated Ca2+ influx by veratridine and high K+ but not that by "Na+-free." Trifluoperazine, a potent calmodulin antagonist, inhibited both Ca2+ influx and ACh release induced by the depolarizing agents. Inhibitory potencies of the two drugs on ACh release and Ca2+ influx were compared with the antagonism of calmodulin by two drugs, suggesting that the inhibition of depolarization-induced Ca2+ influx and ACh release by these drugs could not be explained by the antagonism of calmodulin.

Acetylcholine↗
PubMed1983

Coronary angiographic findings in various types of unstable angina--study on the pathophysiology of unstable angina.

Coronary angiographic findings were studied in 129 patients with various types of unstable angina in order to clarify the pathophysiology of unstable angina. The subjects were divided into 3 types: effort angina (E), rest angina (R), and effort and rest angina (E+R), and each of these 3 types was subdivided into group I (new onset), II (recurrent) and III (changing pattern). 1) R had less severe coronary lesions than E or E+R. 2) Severity and distribution of coronary atherosclerotic lesions in unstable angina were similar to those in stable angina. 3) Incidence of coronary spasm is higher in unstable R and E+R than in stable R and E+R, respectively. 4) Unstable R and E+R with frequent attacks were associated with a higher frequency of coronary spasm and severe proximal coronary stenosis than those without frequent attacks, respectively. 5) Among unstable E+R-III (changing pattern), the patients who developed E+R from E showed significantly higher incidence of multiple vessel disease than those who developed E+R from R and significantly lower incidence of spontaneous spasm than those with E+R, who remained with the same pattern but in whom the frequency and/or the intensity of the attack increased, without any significant difference in the severity of coronary stenosis from other 2 subgroups. It is concluded that coronary spasm as well as severe coronary atherosclerotic lesions may be responsible for the unstable state of angina. Especially in R and E+R, coronary spasm is the most important factor responsible for the unstabilization of angina.

Adult↗
PubMed1983

Behavior of the imino protons of the lambda OR3 17mer studied by high resolution NMR.

Imino proton resonances of lambda OR3 17mer were observed with time-shared Redfield pulse method by using a JEOL 500 MHz NMR instrument. They show gradual broadening and disappearance with the elevation of temperature indicating the stepwise melting of the duplex. By the selective irradiation at each peak position nuclear Overhauser effects were observed between the imino and adenine C2H protons and between imino protons themselves. Combining these data, fifteen imino proton resonances could be assigned to each base pair except two terminal AT base pairs. Based on the assignment it can be said that AT rich regions near the terminal melt first, followed by the melting of the inside GC rich core. The two AT base pairs in the middle of the GC core are resistant to heat. Spin lattice relaxation times were also observed and the results are consistent with the melting profile.

Bacteriophage lambda↗
PubMed1982

Solubilization of adenylate cyclase of brain membranes by lipid peroxidation.

Adenylate cyclase in the membrane fractions of bovine and rat brains, but not in rat liver plasma membranes, was solubilized by treatment with Fe2+ (10 microM) plus dithiothreitol (5 mM). Solubilization of the enzyme by these agents was completely prevented by simultaneous addition of N,N'-diphenyl-p-phenylenediamine (DPPD), an inhibitor of lipid peroxidation. Ascorbic acid also solubilized the enzyme from the brain membranes. Lipid peroxidation of the brain membranes was characterized by a selective loss of phosphatidylethanolamine. Solubilization of membrane-bound enzymes by Fe2+ plus dithiothreitol was not specific for adenylate cyclase, because phosphodiesterase, thiaminediphosphatase and many other proteins were also solubilized. Solubilized adenylate cyclase had a high specific activity and was not activated by either NaF, 5'-guanylyl imidodiphosphate (Gpp[NH]p) or calmodulin. These results suggested that lipid peroxidation of the brain membranes significantly solubilized adenylate cyclase of high specific activity.

Adenylyl Cyclases↗
PubMed1982

Studies on the enzymatic reduction of C-nitroso compounds. V. Molecular properties of porcine heart C-nitrosoreductase and identity of this enzyme with NAD(P)H dehydrogenase.

NAD(P)H-dependent C-nitrosoreductase of porcine heart cytosol was purified 12,000-fold in the presence of NADH with an overall yield of 2.2%. The purification procedure included ammonium sulfate fractionation, gel filtration with Sephadex G-100, ion-exchange chromatography on DEAE-Sephadex A-50, hydrophobic chromatography on Octyl-Sepharose CL-4B, and gel filtration with Sephadex G-200. The purity of the preparation was approximately 90% and the molecular weight of the enzyme estimated by gel filtration was about 60,000. The purified enzyme was composed of two molecular forms, nitrosoreductases 1 and 2, having isoelectric points of 8.45 and 8.6, respectively. A significant amount of zinc was found in the preparation by X-ray fluorescence analysis. The enzyme as it was prepared was colorless, but, after oxidation with p-nitrosophenol followed by gel filtration in the absence of NADH, it showed the absorption spectrum of a flavoprotein. Spectral data indicated the presence of 1 mol of flavin per mol of the enzyme. The molecular turnover number was calculated to be 10,000 nmol p-nitrosophenol reduced to p-aminophenol per min per nmol enzyme at pH 5.8 and 22 degrees C. The activity was inhibited by p-chloromercuribenzoate by 50% at a concentration of 3 x 10(-5) M. Besides the nitrosoreductase activity, the purified preparation showed NAD(P)H-dependent menadione reductase activity. The activities were both strongly inhibited by dicumarol and markedly activated by serum albumin and by Tween 20. These results indicate the probable identity of this enzyme with soluble NAD(P)H dehydrogenase (quinone) [EC 1.6.99.2].

Alcohol Oxidoreductases↗