Search PubMed⌕ Search

Biomedical subjects

D C White

Publications and source records attributed to D C White.

At least 199 records · Page 11Linked to original sources
PubMed1972

Phosphate starvation and the nonlinear dynamics of insect fibrillar flight muscle.

The nonlinear mechanical dynamics of glycerinated insect fibrillar flight muscle are investigated. The most striking nonlinearity reported previously, which often resulted in oscillatory work being limited to frequencies below those of natural flight, disappears if 5 mM or more orthophosphate is added to the experimental solutions. We show that two further asymmetric nonlinearities, which remain even though phosphate is present, are predicted by cross-bridge theory if one takes account of the expected distortion of attached cross-bridges as filament sliding becomes appreciable. Adenosine triphosphate and adenosine diphosphate have opponent effects upon the mechanical rate constants, suggesting a scheme for the sequential ordering of the events comprising the cross-bridge cycle.

Adenosine Diphosphate↗
PubMed1972

Effect of glycerol deprivation on the phospholipid metabolism of a glycerol auxotroph of Staphylococcus aureus.

A study of the effects of glycerol deprivation on the content and metabolism of the phospholipids of a glycerol auxotroph of Staphylococcus aureus showed that (i) there was an increase in the proportions of lysylphosphatidylglycerol (LPB) and a concomitant decrease in the proportion of phosphatidylglycerol. The total phospholipid content per sample and the proportion of cardiolipin did not change, but the phosphatidic acid increased transiently and then fell to pretreatment levels. (ii) The loss of (32)P from the lipids during the chase in a pulse-chase experiment was essentially the same in phosphatidylglycerol, cardiolipin, and phosphatidic acid during glycerol deprivation or growth in the presence of glycerol. LPG lost half the radioactivity in slightly more than two doubling times when grown with glycerol. In the absence of glycerol, (32)P accumulated in LPG for about 20 min and then stopped, after which time there was no apparent turnover. (iii) During glycerol deprivation, the initial (32)P incorporation decreased sixfold compared to that of the control with glycerol. The initial incorporation into LPG decreased only 2.5-fold, whereas that of PG decreased 45-fold. (iv) During glycerol deprivation, the free fatty acid content increased from 1.2 to 12.5% of the total extractable fatty acids and then slowly decreased. The increase was largely iso- and anti-iso-branched 21-carbon-atom fatty acids. In glycerol-supplemented cultures, the major fatty acids were branched 14- to 18-carbon fatty acids. The decrease in longer chain free fatty acids after 60 min represented their esterification into lipids. (v) During glycerol deprivation ribonucleic acid synthesis and cell growth continued for 40 min and protein synthesis continued for 90 min. Then synthesis and growth stopped. (vi) After the addition of glycerol to glycerol-deprived cells, (32)P and (14)C-glycerol were incorporated into the phospholipids without lag; ribonucleic acid, protein synthesis, and cell growth began after a 5- to 10-min lag at the pretreatment rate. The initial rate of lipid synthesis after the addition of glycerol was three times greater than the growth rate. This rapid rate continued for about 25 min until the lipid content and proportions of LPG and phosphatidylglycerol were restored.

Bacterial Proteins↗
PubMed1972

Biosynthesis of cardiolipin from phosphatidylglycerol in Staphylococcus aureus.

Cardiolipin (CL) synthetase from Staphylococcus aureus catalyzes the complete conversion of two molecules of phosphatidylglycerol (PG) to one molecule of CL and one molecule of glycerol. The fatty acids and phosphates of the two PG molecules can be quantitatively recovered in the CL. The enzyme is membrane-bound, shows a linear relationship with the product formed between 10 and 125 mug of membrane protein, has a pH optimum at 4.4, a temperature optimum between 37 and 45 C, a K(m) for PG of 2.1 x 10(-4)m, a V(max) of 200 nmoles of CL per min per mg of membrane protein, and does not require monovalent or divalent metals for activity. The enzyme has no nucleotide requirement and is not affected by prolonged dialysis, and treatment of the enzyme with charcoal has no effect on its activity. The enzyme has no phosphomonoesterase or phosphodiesterase activity, does not act on CL, is specific for PG, and CL and glycerol are the sole products of its activity. Other lipids do not stimulate or inhibit its activity. The enzyme is inhibited by organic solvents and some detergents. There is sufficient CL synthetase activity to account for CL synthesis during exponential growth. Inhibition of CL hydrolysis during growth results in an increase in CL that is balanced by a loss of PG. The activity of CL synthetase is not affected by cytidine diphosphate diglyceride but is inhibited competitively by the product, CL.

Acetates↗
PubMed1972

Consequences of glycerol deprivation on the synthesis of membrane components in a glycerol auxotroph of Staphylococcus aureus.

In a glycerol auxotroph of Staphylococcus aureus, the deprivation of glycerol affected the formation of certain membrane components. (i) There was synthesis of fatty acids at the predeprivation rate even though the fatty acids synthesized accumulated as free fatty acids rather than as esterified fatty acids; (ii) there was a complete cessation of phospholipid and vitamin K isoprenologue biosynthesis; (iii) there was conservation of the glycerol esters of the complex phospholipids and glucolipids; (iv) there was an immediate decrease in the rate of synthesis of monoglucoslydiglyceride (30%) and diglucosyldiglyceride (60%); (v) there was a 50% decrease in the rate of synthesis of the polar and nonpolar carotenoids; (vi) there was synthesis of protoheme, heme a, and nonspecific membrane protein at the predeprivation rate; and (vii) there was an abrupt cessation in the formation of new, functional glycine transport activity.

Acetates↗
PubMed1972

Phospholipid composition and metabolism of Micrococcus denitrificans.

The phospholipid composition of Micrococcus denitrificans was unusual in that phosphatidyl choline (PC) was a major phospholipid (30.9%). Other phospholipids were phosphatidyl glycerol (PG, 52.4%), phosphatidyl ethanolamine (PE, 5.8%), an unknown phospholipid (5.3%), cardiolipin (CL, 3.2%), phosphatidyl dimethylethanolamine (PDME, 0.9%), phosphatidyl monomethylethanolamine (PMME, 0.6%), phosphatidyl serine (PS, 0.5%), and phosphatidic acid (0.4%). Kinetics of (32)P incorporation suggested that PC was formed by the successive methylations of PE. Pulse-chase experiments with pulses of (32)P or acetate-1-(14)C to exponentially growing cells showed loss of isotopes from PMME, PDME, PS, and CL with biphasic kinetics suggesting the same type of multiple pools of these lipids as proposed in other bacteria. The major phospholipids, PC, PG, and PE, were metabolically stable under these conditions. The fatty acids isolated from the complex lipids were also unusual in being a simple mixture of seven fatty acids with oleic acid representing 86% of the total. Few free fatty acids and no non-extractable fatty acids associated with the cell wall or membrane were found.

Autoradiography↗
PubMed1971

Effect of temperature on the fatty acid composition of Thermus aquaticus.

Thermus aquaticus contains four major fatty acids, iso-C(15) (28%), iso-C(16) (9%), normal-C(16) (13%), and iso-C(17) (48%), when grown at 70 C, as determined by gas chromatography and mass spectrometry. Small amounts of iso-C(12), normal-C(12:1), iso-C(13), normal-C(14), iso-C(14), and normal-C(15:1) were also detected. A change in growth temperature (50 to 75 C at 5-C intervals) affects a shift in the proportions of some of the fatty acids. The proportions of the monoenoic and branched-C(17) fatty acids decreased and the proportions of the higher-melting iso-C(16) and normal-C(16) fatty acids increased. Cells grown at 75 C contained 70% more total fatty acids than cells grown at 50 C. The largest increases, in absolute amounts, were in the content of iso-C(16) and normal-C(16) fatty acids, with only a 1.6-fold increase in the major iso-C(15) and iso-C(17) fatty acids. There was a 2.5-fold decrease in normal-C(15:1) and at least a 24-fold decrease in anteiso-C(17), which is present at 50 and 55 C but not at higher temperatures. There was no difference in proportion or amount of fatty acids between exponential and stationary-phase cells grown at 70 C. When cells were grown on glutamate instead of yeast-extract and tryptone at 70 C, the total fatty acid content remained constant, but there was an increase in the proportions of iso-C(16) and normal-C(16) fatty acids concomitant with a decrease in the proportions of the iso-C(15) and iso-C(17) fatty acids.

Bacteria↗
PubMed1971

Effect of benzo(a) pyrene and piperonyl butoxide on formation of respiratory system, phospholipids, and carotenoids of Staphylococcus aureus.

Staphylococcus aureus formed an electron transport system when exponentially growing cells were aerated. Formation of the electron transport system occurred concomitantly with increases in the phospholipids and the carotenoids. The addition of piperonyl butoxide or benzo(a)pyrene at the onset of aeration (i) slowed the formation of the electron transport system, (ii) both inhibited cytochrome oxidase o synthesis and decreased its stability, (iii) simultaneously depressed the increase in total phospholipid (especially cardiolipin), and (iv) depressed the synthesis of the carotenoid rubixanthin. Benzo(a)pyrene was the more inhibitory of the two, both on the rate of synthesis of the electron transport system and on rubixanthin formation. Evidence obtained with the inhibitors suggested that inhibition of the lipid synthesis was related to the formation of the electron transport system.

Benzopyrenes↗
PubMed1971

Phospholipid metabolism in the absence of net phospholipid synthesis in a glycerol-requiring mutant of Bacillus subtilis.

A glycerol-requiring auxotroph of Bacillus subtilis showed no net synthesis of phospholipid when deprived of glycerol. Although there was no net synthesis of phospholipid, we found that: (i) fatty acids and (32)P were slowly incorporated into phospholipid; (ii) in pulse-chase experiments, both (32)P and (14)C in the glycerol portion of the phospholipids were lost from phosphatidlyglycerol (PG) and lysylphosphatidylglycerol and accumulated in cardiolipin (CL); (iii) the proportions of the phospholipids in the membrane changed with a loss of PG and an accumulation of CL. The addition of glycerol to the glycerol-deprived cells resulted in a rapid incorporation of glycerol and restoration to the predeprivation metabolism and PG to CL ratio.

Autoradiography↗
PubMed1971

Metabolism of phosphatidylglycerol, lysylphosphatidylglycerol, and cardiolipin of Staphylococcus aureus.

Staphylococcus aureus accumulated cardiolipin (CL) and lost phosphatidylglycerol (PG) during the stationary phase of growth. The minor lipids, phosphatidylethanolamine and phosphatidylglucose, also accumulated, whereas the lysylphosphatidylglycerol (LPG) content of the membrane remained constant as stationary phase continued. During exponential growth, the proportions and total content of phospholipids per cell remained constant. The metabolism of the phospholipids was examined under these conditions. In pulse-chase experiments, the phospholipids lost (14)C from the glycerols slower than (32)P. When the phospholipids were labeled with (14)C glycerol, the unacylated glycerols of PG and LPG lost (14)C, whereas the diacylated glycerols either accumulated or did not lose (14)C. In all experiments, the PG showed a more rapid metabolism than the LPG. When staphylococcal CL was hydrolyzed by Haemophilus parainfluenzae CL-specific phospholipase D into phosphatidic acid (PA) and PG, the incorporation of (32)P into both of the phosphates of CL was found to be parallel at both the PG and PA ends of the molecule. However, the specific activity of the (32)P at the PA end was twice that at the PG end of the molecule. The PG end of the CL apparently came from a portion of the cellular PG pool with about 20% the specific activity of the total cellular PG. The turnover of two of the glycerols of the PG portion of CL was like that of the cellular PG. The diacylated glycerol of the PG and of CL and of the membrane PG showed neither turnover nor incorporation of (14)C. Half of the radioactivity was lost from the middle glycerol of CL and the free glycerol of the cellular PG in one bacterial doubling. The diacylated glycerol from the other end of the CL molecule (the PA end) lost radioactivity almost as rapidly as the middle glycerol for 10 min. After the initial rapid loss, the turnover slowed to a rate 10 times slower than the middle glycerol, indicating that the (14)C was actually accumulating at this end of the molecule. The phosphates and glycerols involved in the hydrolysis and resynthesis of the CL molecule during exponential growth in S. aureus apparently come from different pools of PG.

Aerobiosis↗