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Biomedical subjects

D C White

Publications and source records attributed to D C White.

At least 235 records · Page 13Linked to original sources
PubMed1970

Phospholipid metabolism during penicillinase production in Bacillus licheniformis.

During membrane-bound penicillinase production, Bacillus licheniformis forms vesicles and tubules that do not appear in the absence of penicillinase production. The major lipids of B. licheniformis were shown to be phospholipids. The proportions, metabolism, and the total phospholipid per cell were shown to be essentially the same in the uninduced control, induced and constitutive penicillinase forming cells during both the exponential and stationary growth phases. Membrane phospholipids were not secreted into the medium during penicillinase formation. In the shift from the exponential to the stationary growth phase, there was an accumulation of phosphatidyl glycerol and a marked decrease in cardiolipin. These two lipids had the most active turnover of their phospholipid phosphate of all the lipids studied.

Bacillus↗
PubMed1970

Changes in membrane lipid composition in exponentially growing Staphylococcus aureus during the shift from 37 to 25 C.

Lowering the temperature of growth of Staphylococcus aureus from 37 to 25 C decreased the growth rate and induced changes in the composition of the membrane lipids. Changes in lipid composition also occur in the transition between exponential and stationary growth phases at one temperature. To isolate the effects of lowering the temperature, exponentially growing S. aureus was abruptly switched from 37 to 25 C by transfer to cooler medium. Exponential growth continued at 25 C without a lag period but with a threefold increase in doubling time. In the period of exponential growth at suboptimal temperature, there was essentially no change in the fatty acid composition of the lipids, little change in the vitamin K(2) composition with perhaps a slight increase in the total level, and essentially no change in the phospholipid composition, but a marked stimulation of the synthesis of the rubixanthins. Growth of cells at 25 C was much more sensitive to the inhibition of rubixanthin formation by mixed-function oxidase inhibitors than cells growing at 37 C, suggesting some function for the rubixanthins at suboptimal temperatures. The striking increases in the proportions of monoenoic fatty acids observed at lowered growth temperatures in many biological systems are not detected in S. aureus.

Carotenoids↗
PubMed1970

Cardiolipin-specific phospholipase D of Haemophilus parainfluenzae. II. Characteristics and possible significance.

A phospholipase specific for cardiolipin (CL) was found in the membrane of Haemophilus parainfluenzae. The enzyme hydrolyzed CL to phosphatidic acid (PA) and phosphatidylglycerol (PG), indicating that it was a phospholipase D (an enzyme activity believed to be confined to higher plants). In addition to its substrate specificity, this enzyme was unusual in its requirement for Mg(2+) (K(m) of 1.3 mm) for maximal activity and its inhibition by chelating agents, heavy metals, some detergents, and organic solvents. When inhibitors of phospholipase activity were added to the growth medium, CL accumulated and PG disappeared in the membrane, suggesting that the phospholipase D was active in vivo. The activity of phospholipase D in cell-free homogenates was greater than expected from earlier studies of CL metabolism and greater than the other phospholipase activities detected in the homogenate. The high activity of the CL-specific phospholipase D suggests there might be a very active degradation of CL to PG and PA and an active resynthesis of CL from the hydrolysis products.

Autoradiography↗
PubMed1969

Distributed representations for actin-myosin interaction in the oscillatory contraction of muscle.

In this paper we suggest and test a specific hypothesis relating the attachment-detachment cycle of cross bridges between actin (I) and myosin (A) filaments to the measured length-tension dynamics of active insect fibrillar flight muscle. It is first shown that if local A-filament strain perturbs the rate constants in the cross-bridge cycle appropriately, then exponentially delayed tension changes can follow imposed changes of length; the latter phenomenon is sufficient for the work-producing property of fibrillar muscle, as measured with small-signal forcing of length and at low Ca(2+) concentration, and possibly for related effects described recently in frog striated muscle. It is not clear a priori that the above explanation of work production by fibrillar muscle will remain tenable when the viscoelastic complexity of the heterogeneous sarcomere is taken into account. However, White's (1967) recent mechanical and electron microscope study of the passive dynamics of glycerinated fibrillar muscle has produced a model of the distributed viscoeleastic structure sufficiently explicit that alternative schemes for cross-bridge force generation in this muscle can now be tested more critically than previously. Therefore, we derive and solve third-order partial-differential equations which relate local interfilament shear forces associated with the perturbed cross-bridge cycles to the over-all length-tension dynamics of an idealized sarcomere. We then show (a) that the starting hypothesis can account approximately for the small-signal dynamics of glycerinated muscle in the work-producing state over two decades of frequency and (b) that the rate constants for cross-bridge formation and breakage, restricted solely by fitting of the model to the mechanical data, determine a cycling rate of cross bridges in the model compatible with recent measurements of ATP hydrolysis rate vs. stretch in this muscle. Finally, the formulation is extended tentatively to the large-signal nonlinear case, and shown to compare favorably with previous suggestions for the origin of the work-producing dynamics of fibrillar flight muscle.

Adenosine Triphosphate↗
PubMed1969

Mechanical properties of glycerinated fibres from the tymbal muscles of a Brazilian cicada.

1. Some of the properties of glycerinated fibres from the synchronous tymbal muscles of the cicada Fidicina rana have been investigated.2. In the presence of suitable concentrations of ATP and calcium ions, the fibres are able to perform oscillatory work when subjected to small sinusoidal length changes in the frequency range 2-30 c/s.3. When subjected to abrupt changes in length, active fibres show a delayed increase in tension after a stretch and a delayed decrease in tension after release.4. The muscle fibres therefore show the mechanical properties characteristic of glycerinated fibres from asychronous insect flight muscles. Some implications of this finding in relation to the evolution of asynchronous muscles are discussed.

Adenosine Triphosphate↗
PubMed1969

Formation of vitamin K2 isoprenologues by Staphylococcus aureus.

In Staphylococcus aureus, vitamin K(2) isoprenologues can be labeled with (14)C-acetate, mevalonate, glycerol, alpha-naphthol, and menadione. All the radioactivity from alpha-naphthol is in the ring nucleus. Eighty-six per cent of the radioactivity from mevalonate is in the side chain. The labeled isoprenologues of vitamin K(2) can be separated and recovered quantitatively. The rates of incorporation and turnover after pulse-chase experiments indicate that the isoprenologues do not lose radioactivity once they are formed. The kinetics of incorporation of radioactivity into the ring nucleus of each isoprenologue are the same. The alkylation of the ring does not involve a simple sequential addition of isoprenoid units of the same specific activity. The incorporation of mevalonate shows that shorter side chain isoprenologues have a higher specific activity per five carbon unit than the longer side chain isoprenologues. Perhaps the alkyl precursors are from different pools since the kinetics of incorporation into all isoprenologues are different.

Carbon Isotopes↗
PubMed1969

Phospholipid metabolism during changes in the proportions of membrane-bound respiratory pigments in Haemophilus parainfluenzae.

After a transition from high to low oxygen tension, there was a twofold to 50-fold increase in the content of membrane-bound respiratory pigments of Haemophilus parainfluenzae, and there were concurrent changes in the metabolism of the membrane phospholipids: (i) a twofold decrease in the rate of turnover of the phosphate in all the phospholipids; (ii) a shift from simple one-phase, linear incorporation of phosphate into phospholipids to a complex biphasic incorporation of phosphate into phospholipids; and (iii) an increase in the total phospholipids with a slight increase in the proportion of phosphatidylglycerol (PG) and a slight decrease in the proportion of phosphatidylethanolamine (PE). Changes in the rates of incorporation of phosphate into the phospholipids occurred without a change in the rate of bacterial growth. When the compensatory adjustment of the proportions of the respiratory pigments reached a steady state, the total phospholipid, the rate of incorporation of phosphate into phospholipids, and the proportion of PG fell. At steady-state proportions of cytochromes, the proportion of PE and the rate of turnover of the phosphate in the phospholipids increased. All through an incorporation experiment of 1.5 divisions, the specific activity of the phosphate of PG was twice that of phosphatidic acid (PA). The phosphate of PG turned over 1.2 to 1.5 times more rapidly than the phosphate of PA in cells with high and low cytochrome levels. If the PA was an accurate measure of the precursor for the cytidine-5'-diphosphate-diglyceride, which in turn was the precursor of all the lipids, then the results of these experiments suggested that exchange reactions, in addition to synthesis from PA, were involved in phospholipid metabolism. These reactions were more sensitive to changes in oxygen concentration than was the growth rate.

Amino Alcohols↗
PubMed1969

Phospholipid metabolism in Ferrobacillus ferrooxidans.

The lipid composition of the chemoautotroph Ferrobacillus ferrooxidans has been examined. Fatty acids represent 2% of the dry weight of the cells and 86% of the total are extractable with organic solvents. About 25% of the total fatty acids are associated with diacyl phospholipids. Polar carotenoids, the benzoquinone coenzyme Q-8, and most of the fatty acids are present in the neutral lipids. The phospholipids have been identified as phosphatidyl monomethylethanolamine (42%), phosphatidyl glycerol (23%), phosphatidyl ethanolamine (20%), cardiolipin (13%), phosphatidyl choline (1.5%), and phosphatidyl dimethylethanolamine (1%) by chromatography of the diacyl lipids, by chromatography in four systems of the glycerol phosphate esters derived from the lipids by mild alkaline methanolysis, and by chromatographic identification of the products of acid hydrolysis of the esters. No trace of phosphatidylserine (PS), glycerolphosphorylserine, or serine could be detected in the lipid extract or in derivatives of that extract. This casts some doubt on the postulated involvement of PS in iron metabolism. After growth in the presence of (14)C and (32)P, there was essentially no difference in the turnover of either isotope in the glycerolphosphate ester derived from each lipid in cells grown at pH 1.5 or 3.5.

Autoradiography↗
PubMed1969

Phospholipid metabolism during bacterial growth.

Haemophilus parainfluenzae incorporates glycerol and phosphate into the membrane phospholipids without lag during logarithmic growth. In phosphatidyl glycerol (PG), the phosphate and unacylated glycerol moieties turn over and incorporate radioactivity much more rapidly than does the diacylated glycerol. At least half the radioactivity is lost from the phosphate and unacylated glycerol in about 1 doubling. The total fatty acids turn over slightly faster than the diacyl glycerol. In phosphatidyl ethanolamine (PE), which is the major lipid of the bacterium, ethanolamine and phosphate turn over and incorporate radioactivity at least half as fast as the phosphate in PG. The glycerol of PE did not turn over in 4 bacterial doublings. In phosphatidic acid the glycerol turns over at one-third the rate of phosphate turnover. By means of a modified method for the quantitative recovery of 1,3-glycerol diphosphate from cardiolipin, the phosphates and middle glycerol of cardiolipin were shown to turn over more rapidly than the acylated glycerols during bacterial growth. There is no randomization of the radioactivity in the 1- and 3-positions of the glycerol in the course of 1 doubling. The fatty acids of PG turn over faster than those in PE. In both lipids the 2-fatty acids turn over much faster than the 1-fatty acids. At both positions the individual fatty acids have their own rates of turnover. The distribution of fatty acids between the 1- and 2-positions is the same as in other organisms, with more monoenoic and long-chain fatty acids at the 2-position. The different rates of turnover and incorporation of radioactivity into different parts of the lipids suggest that exchange reactions may be important to phospholipid metabolism.

Amino Alcohols↗
PubMed1969

Identification of ceramide phosphorylethanolamine and ceramide phosphorylglycerol in the lipids of an anaerobic bacterium.

Nearly half the phospholipids isolated from the anerobic bacterium Bacteroides melaninogenicus are phosphosphingolipids. The two major phosphosphingolipids have been characterized as ceramide phosphorylethanolamine and ceramide phosphorylglycerol. The long-chain bases of these phosphosphingolipids appear to have branched and normal saturated carbon chains of 17, 18, and 19 atoms; the phosphate is at the 1-position of the long-chain base. The composition of the amide-linked fatty acids of the phosphosphingolipids differs from that of the ester-linked fatty acids of the diacylphosphoglycerides in having a higher percentage of 14:0, 17:0, and 18:0 acids as well as containing nearly all the monoenoic fatty acids found in the bacterial lipids. The finding of phosphosphingolipids in bacteria is exceedingly rare and to our knowledge ceramide phosphorylglycerol has not been previously found in nature.

Amino Alcohols↗