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Biomedical subjects

M Alexander

Publications and source records attributed to M Alexander.

At least 415 records · Page 23Linked to original sources
PubMed1970

Rapid detection of bacteremia in mice by gas chromatography.

Gas chromatography of the serum of mice inoculated 6 hr earlier with Staphylococcus aureus, Escherichia coli K-12, and Clostridium chauvoei revealed the formation of products associated with the infections. Longer periods were required before compounds resulting from infecting the animals with Salmonella typhimurium and other Clostridium species were detected by gas chromatographic means. The technique is sensitive to the presence of metabolites elaborated in vivo as a result of the presence of 100 to 35,000 cells. Each bacterial species caused the formation of distinctive compounds in infected mice, and substances chromatographically identical to these products were generated by the microorganisms in vitro as well.

Journal Article↗
PubMed1970

Metabolism of sphingolipids by normal and atherosclerotic aorta of squirrel monkeys.

We studied the synthesis and hydrolysis of sphingomyelin by homogenates of aortic intima plus inner media from normal squirrel monkeys and from monkeys with nutritionally-induced atherosclerosis (6-10 mo on a semi-purified diet containing butter and cholesterol). The concentrations of sphingomyelin in the aortas and plasmas of the atherosclerotic monkeys were higher than those for the normal monkeys. Palmitoyl-1-(14)C coenzyme A was actively utilized for the synthesis of ceramide (N-palmitoyl sphingosine). The addition of sphingosylphosphorylcholine increased the utilization of palmitoyl CoA in sphingomyelin synthesis, and the addition of psychosine (sphingosyl galactoside) increased the incorporation of palmitate into cerebrosides. Rates of sphingomyelin and ceramide synthesis were significantly higher in the atherosclerotic than in the control aortas. Hydrolysis of labeled sphingomyelin to ceramide was also increased in homogenates of the atherosclerotic aortas. Labeled sphingomyelin was taken up from plasma by everted carotid arteries, and this process was also enhanced by atherosclerosis. Increased rates of synthesis and of uptake from plasma of sphingomyelin may account for the increased concentrations of sphingomyelin in the atherosclerotic arteries, even though the ability to degrade sphingomyelin is also enhanced in the atherosclerotic aorta.

Animals↗
PubMed1970

Metabolism of lysolecithin in vivo: effects of hyperlipemia and atherosclerosis in squirrel monkeys.

We have studied the effect of long-term hyperlipemia and atherosclerosis in squirrel monkeys on the metabolism of lysolecithin-(14)C (1-palmitoyl-1'-(14)C sn-glycerol 3-phosphorylcholine) in order to explain elevated plasma and arterial concentrations of lysolecithin. The die-away curves of lysolecithin-(14)C from plasma and the timing of appearances of other (14)C-labeled moieties in plasma and other tissues demonstrated a complex pattern of metabolic reactions. There was a rapid equilibration of specific activities of lysolecithin of plasma, liver, and aortic intima plus inner media. The specific activities of lecithin peaked first in liver, then in plasma, and rose slowly in aortic intima plus inner media. The appearance of lecithin-(14)C in heart and skeletal muscle was also slower than in the liver and some other tissues. Triglycerides, and to a lesser extent, cholesteryl esters contained radioactivity. The concentrations of aortic lysolecithin in the atherosclerotic aortas were several times greater than comparable values for control aortas, and the time of equilibration of plasma and aorta lysolecithin-(14)C was much greater for the atherosclerotic group. The quantities of lysolecithin in plasma and in the pool of which the plasma was a part, were increased with hyperlipemia and atherosclerosis, as was the rate of lysolecithin production in the fast pool. Hyperlipemia was also associated with an early increase in plasma lecithin:cholesterol acyltransferase (LCAT) activity in vitro. Furthermore, nutritional hyperlipemia influenced the distribution of lysolecithin-(14)C and lecithin-(14)C between different plasma lipoproteins. The increase in concentrations of lysolecithin in the aorta occurred more slowly than that in plasma after we had induced hyperlipemia in the monkeys.

Acyltransferases↗
PubMed1969

Cometabolism and gas chromatography for the sensitive detection of bacteria.

Salmonella typhimurium, Escherichia coli, and Staphylococcus aureus were grown in media containing one of several halogenated organic acids which the bacteria metabolized but could not use as a major carbon and energy source for growth. Gas chromatographic techniques were employed to detect the presence of low population densities by analysis for products formed by the microorganisms. By virtue of the presence of the cometabolizable halogenated substrate in the medium, the sensitivity of procedures for detecting the presence of S. typhimurium, E. coli, and S. aureus was increased more than 7,000-, 20,000-, and 1,000-fold, respectively.

Acetates↗
PubMed1969

Cell walls and lysis of Mortierella parvispora hyphae.

Walls of Mortierella parvispora, Pullularia pullulans, Absidia repens, Fusarium oxysporum, and of several Penicillium species varied in their susceptibilities to digestion by glucanase and chitinase. Polysaccharides were present in the residues remaining after enzymatic digestion. Acid hydrolysates of the walls contained glucose, glucosamine, and a small amount of galactose. The walls of M. parvispora, which also contained fucose, were the least digested by these two enzymes. Much of the M. parvispora wall material was resistant to decomposition by a heterogeneous soil community, and viable hyphae were not lysed by a glucanase-chitinase mixture. Walls of this fungus were fractionated, and the chemical composition of the fractions was determined. The chitin which was abundant in one of the fractions was apparently largely shielded from chitinase hydrolysis by a glucan. The ecological significance of these findings is discussed.

Basidiomycota↗
PubMed1969

Lysophosphatidylcholine concentrations and metabolism in aortic intima plus inner media: effect of nutritionally induced atherosclerosis.

The concentration of lysophosphatidylcholine (monoacyl sn-glycerol 3-phosphorylcholine) in intima plus inner media of atherosclerotic aorta from squirrel monkeys was nearly eight times that in comparable control tissue. Plasma levels of the same compound were somewhat elevated in the atherosclerotic group. The metabolism of fatty acyl CoA's and lysophosphatides was studied in cell-free preparations of intima plus inner media from squirrel monkey aorta. Linoleic acid was incorporated predominantly into phosphatidylcholine (as opposed to other phospholipids) when linoleoyl-1-(14)C CoA was the substrate. The extent of this reaction was dependent on the concentration of lysophosphatidylcholine. Lysophosphatidylethanolamine (monoacyl sn-glycerol 3-phosphorylethanolamine) stimulated the incorporation of linoleate into phosphatidylethanolamine. 1-Palmitoyl-1'-(14)C sn-glycerol 3-phosphorylcholine ((14)C-lysophosphatidylcholine) was incorporated into phosphatidylcholine only in the presence of acyl CoA's or ATP plus CoA. Incorporation of (14)C with (14)C-lysophosphatidylcholine plus linoleoyl CoA equaled that with linoleoyl-1-(14)C CoA and lysophosphatidylcholine. Various other lines of evidence are presented to support the importance of the fatty acyl CoA:lysophosphatide fatty acyl transferase mechanism in aortic phospholipid metabolism. Cell-free preparations of aortic intima plus inner media from squirrel monkeys with early, nutritionally-induced atherosclerosis utilized linoleoyl-1-(14)C CoA more than preparations from control monkeys when incubations were carried out without added lysophosphatidylcholine and for long periods (30 min). With optimum levels of labeled linoleoyl CoA and unlabeled lysophosphatidylcholine, or unlabeled linoleoyl CoA and labeled lysophosphatidylcholine, there were no differences in substrate utilization between control and atherosclerotic tissues. We conclude that the concentrations of lysophosphatidylcholine, which are higher in atherosclerotic than in control aortic tissues, could be a factor controlling rates of fatty acid incorporation into phosphatidylcholine.

Acyltransferases↗