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Biomedical subjects

B Shapiro

Publications and source records attributed to B Shapiro.

At least 379 records · Page 21Linked to original sources
PubMed1968

Studies on medium-chain fatty acyl-coenzyme a synthetase. Purification and properties.

1. Medium-chain fatty acyl-CoA synthetase (EC 6.2.1.2) was isolated by the method of Mahler, Wakil & Bock (1953) and the enzyme activity determined by the disappearance of CoA in the presence either of butyrate and ATP or of butyryl-AMP, as well as by ATP formation from butyryl-AMP and PP(i). 2. Preincubation of the enzyme with CoA and ATP alone or together, followed by the removal of these substrates by gel filtration, caused a marked inhibition of ATP formation, contrary to results previously obtained with palmitoyl-CoA synthetase. 3. The effect of ATP on butyryl-AMP-dependent CoA disappearance was inconsistent. Low concentrations of ATP (0.1-0.5mm) always caused inhibition, whereas higher concentrations (5-10mm) activated in some enzyme preparations and inhibited in others. 4. This inconsistency was shown to be due to the presence of two enzyme fractions. Both fractions had similar activities when assayed by the butyryl-AMP- or butyrate-plus-ATP-dependent CoA disappearance. However, fraction I was activated by ATP as measured by butyryl-AMP-dependent CoA disappearance whereas fraction II was inhibited by it. Fraction I also catalysed ATP formation from butyryl-AMP and PP(i) whereas fraction II was lacking in such activity. 5. The relationship of these observations with respect to other known mechanisms of fatty acid-activating systems is discussed.

Adenine Nucleotides↗
PubMed1967

Effect of propionate on lipogenesis in adipose tissue.

The metabolism of propionate in adipose tissue and its effect on lipogenesis was investigated. Fasting induced changes in propionate metabolism of adipose tissue, drastically reducing higher fatty acid synthesis and increasing glyceride-glyerol formation from low concentrations of propionate (0.25 mM). Propionate also promoted lipogenesis from acetate-1-(14)C in tissues of fasted rats, while it inhibited lipogenesis and CO(2) formation from acetate in the fed animal. Treatment with actinomycin D or ethionine abolished both the increased glyceride-glycerol formation from propionate and the promoting effect on lipogenesis from acetate. Synthesis of long-chain fatty acids from propionate-1-(14)C was increased by actinomycin treatment. The change in propionate metabolism induced by fasting is, however, not entirely due to its conversion to glyceride-glycerol, since the latter was almost completely blocked by malonate while part of the promoting effect on fatty acid synthesis persisted.

Acetates↗
PubMed1967

Effect of propionate on pyruvate metabolism in adipose tissue.

Glyceride-glycerol formation in rat adipose tissue from pyruvate-2-(14)C is increased by fasting, while fatty acid synthesis is markedly depressed. In tissues of fasted animals glyceride-glycerol formation is maximal with concentrations of pyruvate exceeding 2.5 mM. With 0.25 mM pyruvate-2-(14)C, glyceride-glycerol formation is increased severalfold by the addition of 0.25 mM propionate. No further increase in synthesis is caused by propionate when pyruvate is supplied in optimal amounts. Addition of equimolar concentrations of acetate or pyruvate does not replace propionate. The effect of propionate on glyceride-glycerol synthesis from pyruvate is also given by a series of even-chain fatty acids. However, only propionate promotes fatty acid synthesis in tissues of fasted and fed animals. Fixation of (14)CO(2) in glyceride-glycerol is dependent on the presence of propionate and is maximal in tissues of fasted rats and when pyruvate is also added. Succinate has no significant effect. Actinomycin treatment blocks glyceride-glycerol synthesis in tissues of fed and fasted animals, in the presence and absence of propionate. At the same time, fatty acid synthesis in tissues of fasted rats is markedly increased.

Adipose Tissue↗
PubMed1966

Enzymic hydrolysis of sphingomyelin by rat liver.

1. An enzyme that hydrolyses sphingomyelin to ceramide (N-acylsphingosine) and phosphorylcholine was isolated from rat liver. 2. The enzyme is particle-bound (mitochondria or lysosomes) and can be solubilized by ultrasonic treatment and freezing and thawing. 3. It has been partially purified by precipitation at pH5.2, neutralization and ammonium sulphate fractionation. 4. The enzyme is activated by Triton X-100 (0.2%) or low concentrations of cetyltrimethylammonium bromide (0.02%), higher concentration being inhibitory. 5. The optimum pH is 5-5.5. 6. Of synthetic substrates tested, the erythro isomers of dl-trans-2-N-palmitoyl-1-O-phosphorylcholinesphingosine or dihydrosphingosine were hydrolysed at a rate similar to the natural compound. The threo isomer was hydrolysed much more slowly. The enzyme had little activity on lecithin. 7. The split products of the hydrolysis have little inhibitory effect.

Amino Alcohols↗