Incorporation of fatty acids into the outer and inner membranes of isolated rat liver mitochondria

Acyl-CoA: phospholipid acyl-transferase activity as well as phospholipase A activity were detected in inner and outer membrane preparations from rat liver mitochondria. Both enzyme systems have an optimum pH around 8 and act preferentially on phosphatidylethanolamine. While phospholipase A activity is much lower in the inner membrane than in the outer membrane of mitochondria the reverse is true for the incorporation of (14C)-oleic acid into endogenous phosphatidylethanolamine. These results bring an indirect evidence that the inner membrane per se possesses a phospholipase A activity.     

An acetaldehyde dehydrogenase from germinating seeds

An acetaldehyde dehydrogenase from germinating peanut cotyledons has been purified and its properties have been studied. At the highest purification achieved the preparation is free of alcohol dehydrogenase activity.

The enzyme is specific toward diphosphopyridine nucleotide, and can oxidize a variety of aldehydes. The highest reaction rate is obtained with acetaldehyde, which is oxidized to acetate. All the attempts to demonstrate the formation of an energy-rich acetyl derivative during the course of the reaction failed. The enzyme is inhibited by aldol; it is sensitive toward sulfhydryl reagents, including arsenite. Reduced glutathione stabilizes the enzyme, while cysteine, mercaptoethanol, and coenzyme A are inhibitory.

Acetaldehyde dehydrogenase is activated by phosphate and inhibited by fatty acyl-CoA derivatives. It appears to be activated by the substrate, as was deduced from the shape of the plot of reaction velocity against acetaldehyde. These properties suggest that the enzyme is an allosteric protein.

The plot of reaction velocity against substrate concentration is anomalous. The shape of this plot seems to reflect the presence of 2 different enzymatic activities, one with extremely high apparent affinity for acetaldehyde. The 2 activities may reflect 2 conformational states of a single enzyme or 2 separate enzymes.

Experiments with tissue slices indicate that the reaction catalyzed by this enzyme is a step in the oxidation of ethanol to acetyl-CoA. This enzyme may also participate in the oxidation of pyruvate to acetyl-CoA in certain tissues.

     

Isolation of a Mutant of Escherichia coli with a Temperature-sensitive Fructose-1,6-Diphosphate Aldolase Activity

B?ck, August (Purdue University, Lafayette, Ind.), and Frederick C. Neidhardt. Isolation of a mutant of Escherichia coli with a temperature-sensitive fructose-1,6-diphosphate aldolase activity. J. Bacteriol. 92:464-469. 1966.-A mutant of Escherichia coli was isolated which was able to grow in rich medium at 30 C but not at 40 C. Upon exposure to 40 C, the cells immediately stopped ribonucleic acid (RNA) and deoxyribonucleic acid synthesis, but protein synthesis continued at a diminished rate for a short time. Addition of chloramphenicol did not release RNA synthesis from inhibition at 40 C. Synthesis of beta-galactosidase could be induced at high temperature despite the presence of glucose in the medium, indicating a lesion in glucose catabolism. Of many catabolic enzymes tested in cell-free extracts, only fructose-1,6-diphosphate aldolase activity appeared to be altered in the mutant cells. No activity was demonstrable in extracts of mutant cells grown at either 30 or 40 C, but determination of glucose-oxidation patterns revealed that the enzyme is probably active in vivo at 30 C. Temperature-resistant secondary mutants were found to have partially or fully restored aldolase activity, and temperature-resistant recombinants had normal aldolase activity, indicating that the growth pattern and the altered aldolase had a common genetic basis. Linkage data permitted the assignment of an approximate map location for the mutated aldolase gene.     

Effect of retinoic acid on the proliferation and tumorigenicity of mouse mastocytoma cells

Retinoic acid (RA) inhibited the in vitro growth of the mouse mast cell tumor line P₈₁₅ in a dose- and time-dependent manner. The inhibition was accompanied by an increase in the amount of neutral intracellular mucopolysaccharides. Study of cell cycle kinetics showed that exposure to retinoic acid led to a slowing-down of the cell-cycle progression possibly related to a more differentiated cell population disclosed by microscopy with a lower proliferative capacity. In vivo, delays in both tumor appearance and mouse mortality were observed after injecting RA into mice bearing mastocytomas. These results suggest that RA could be of interest in the treatment of human malignant systemic mastocytosis with proliferation of immature mast cells.