Reverse electron transfer from the cytochrome c level in cyanide-resistant mitochondria of the yeast, Candida lipolytica]

The ability of cyanide-resistant mitochondria of yeast Candida lipolytica to perform reverse electron transfer from cytochrome c to alternative oxidase was studied. It was shown that the energy for such a transfer can be provided by high energy intermediates or membrane potential but not by ATP. Reverse electron transfer from cytochrome c is impossible due to energy of NADH and alpha-glycerophosphate oxidation via alternative pathway in the presence of cyanide. These results prove once again that electron transfer via alternative pathway is not connected with the energy accumulation.     

Biosynthesis of Naphthoquinone Pigments by Fungi of the Genus Fusarium

Applied Biochemistry and Microbiology - We studied the biosynthesis of colored naphthoquinone metabolites by Fusarium decemcellulare, F. graminearum, and F. bulbigenum fungi. Depending on the...     

Peripartum Cardiomyopathy Presenting With Ventricular Tachycardia: A Rare Presentation

A 25-year-old previously asymptomatic pregnant woman at 36 weeks'' gestation was noticed to have repetitive monomorphic ventricular tachycardia. A dilated left ventricle with moderately reduced systolic function was found on echocardiographic examination. This is a very rare presentation of peripartum cardiomyopathy (PPCMP) presenting with repetitive monomorphic ventricular tachycardia.     

Development and activation of cyanide-resistant respiration in the yeast Yarrowia lipolytica.

Changes in respiratory activity and in the contents of adenine nucleotides (ATP, ADP, AMP) were studied in cells of the yeast Yarrowia lipolytica during the development of cyanide-resistant respiration. The transition of the yeast from the logarithmic to the stationary growth phase due to exhaustion of glucose was associated with decreased endogenous respiration and with the activation of a cyanide-resistant oxidase. Cyanide activated cell respiration during the stationary growth phase. The cyanide-resistant respiration was inhibited by benzohydroxamic acid (BHA), an inhibitor of the alternative oxidase. In the absence of cyanide, BHA had no effect on the cells which had the cyanide-resistant oxidase. This indicates that the cells do not use the alternative pathway in vivo. The decreased endogenous respiration of the cells was accompanied by decreased contents of adenine nucleotides. Addition of cyanide resulted in a sharp decrease in the content of ATP, in a twofold increase in the content of ADP, and in a fivefold increase in the content of AMP. In the absence of cyanide, BHA had virtually no effect on the contents of adenine nucleotides. The decreased rate of oxygen consumption during the transition of the cells to the stationary growth phase was caused by the decreased activity of the main cytochrome-containing respiratory chain (2,4-dinitrophenol (DNP) stimulated respiration). The alternative oxidase was synthesized in the cell but was inactive. Cyanide stimulated respiration due to activation of the alternative oxidase via the AMP produced. The decrease in the cell content of ATP is suggested to be a factor inducing the synthesis of the alternative oxidase.     

Processing of viral envelope glycoprotein by the endomannosidase pathway: evaluation of host cell specificity

Endo-alpha-D-mannosidase is an enzyme involved in N-linked oligosaccharide processing which through its capacity to cleave the internal linkage between the glucose-substituted mannose and the remainder of the polymannose carbohydrate unit can provide an alternate pathway for achieving deglucosylation and thereby make possible the continued formation of complex oligosaccharides during a glucosidase blockade. In view of the important role which has been attributed to glucose on nascent glycoproteins as a regulator of a number of biological events, we chose to further define the in vivo action of endomannosidase by focusing on the well characterized VSV envelope glycoprotein (G protein) which can be formed by the large array of cell lines susceptible to infection by this pathogen. Through an assessment of the extent to which the G protein was converted to an endo-beta-N- acetylglucosaminidase (endo H)-resistant form during a castanospermine imposed glucosidase blockade, we found that utilization of the endomannosidase-mediated deglucosylation route was clearly host cell specific, ranging from greater than 90% in HepG2 and PtK1 cells to complete absence in CHO, MDCK, and MDBK cells, with intermediate values in BHK, BW5147.3, LLC-PK1, BRL, and NRK cell lines. In some of the latter group the electrophoretic pattern after endo H treatment suggested that only one of the two N-linked oligosaccharides of the G protein was processed by endomannosidase. In the presence of the specific endomannosidase inhibitor, Glcalpha1-->3(1- deoxy)mannojirimycin, the conversion of the G protein into an endo H- resistant form was completely arrested. While the lack of G protein processing by CHO cells was consistent with the absence of in vitro measured endomannosidase activity in this cell line, the failure of MDBK and MDCK cells to convert the G protein into an endo H-resistant form was surprising since these cell lines have substantial levels of the enzyme. Similarly, we observed that influenza virus hemagglutinin was not processed in castanospermine-treated MDCK cells. Our findings suggest that studies which rely on glucosidase inhibition to explore the function of glucose in controlling such critical biological phenomena as intracellular movement or quality control should be carried out in cell lines in which the glycoprotein under study is not a substrate for endomannosidase action.      

A compact from of methylated DNA is solutions containing poly (ethylene glycol).

Some peculiarities of compactization of double-stranded DNA molecules containing methylated nitrogen bases have been studied in water-salt solutions of PEG. It is shown that the methylation of N7-atoms of guanyl residues in original DNA molecules does not prevent the formation of DNA compact particles, but results in a decrease of the amplitude of the negative band in the CD spectrum of compact particles. The influence of N7-guanine methylation on the shape of the CD spectrum being the greater, the lower is the concentration of PEG. The dependence of the negative band amplitude in the CD spectrum on the content of methylated guanyl residues is practically the same for low-molecular weight DNA's from different sources. The observed decrease in the negative band amplitude is interpreted as a result of alterration of guanyl residue orientation relative to the helix axis which leads to diminished optical activity of the "microcrystalline" domains of compact particles. The evidence obtained suggests that changes in the secondary structure of DNA lead to considerable difference between CD spectra of compact particles of methlated DNA and psi-form of DNA. (The changes in the CD spectrum of the DNA compact particles occur also as a result of methylation of C5-atoms of cytosine residues). It is suggested that the negative band in the CD spectrum can be used a criterion for detection of negligible alterations in the DNA secondary structure.     

Adaptation of the yeast Yarrowia lipolytica to heat shock

The adaptive response of the yeast Yarrowia lipolytica to heat shock has been studied. Experiments showed that, after 10 min of incubation at 45 degrees C, the survival rate of Yarrowia lipolytica cells was less than 0.1%. Stationary-phase yeast cells were found to be more thermotolerant than exponential-phase cells. The 60-min preincubation of cells at 37 degrees C or pretreatment with low concentrations of H2O2 (0.5 mM) and menadione (0.05 mM) made them more tolerant to heat and to oxidative stress (120 mM hydrogen peroxide). The pH dependence of yeast thermotolerance has also been studied. The adaptation of yeast cells to heat shock and oxidative stress was found to be associated with a decrease in the intracellular level of cAMP and an increase in the activity of antioxidant enzymes (catalase, superoxide dismutase, glucose-6-phosphate dehydrogenase, and glutathione reductase).     

Adaptation of the yeast <Emphasis Type="Italic">Yarrowia lipolytica</Emphasis> to heat shock

The adaptive response of the yeast Yarrowia lipolytica to heat shock has been studied. Experiments showed that, after 10 min of incubation at 45°C, the survival rate of Yarrowia lipolytica cells was less than 0.1%. Stationary-phase yeast cells were found to be more thermotolerant than exponential-phase cells. A 60-min preincubation of cells at 37°C or pretreatment with low concentrations of H₂O₂ (0.5 mM) or menadione (0.05 mM) made them more tolerant to heat and to oxidative stress (120 mM hydrogen peroxide). The pH dependence of yeast thermotolerance has also been studied. The adaptation of yeast cells to heat shock and oxidative stress was found to be associated with a decrease in the intracellular level of cAMP and an increase in the activity of antioxidant enzymes (catalase, superoxide dismutase, glucose-6-phosphate dehydrogenase, and glutathione reductase).