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Biomedical subjects

M A Lea

Publications and source records attributed to M A Lea.

At least 91 records · Page 5Linked to original sources
PubMed1966

Feedback inhibition of key glycolytic enzymes in liver: action of free fatty acids.

Increasing concentrations of sodium octanoate were progressively inhibitory to the activities of glucokinase, hexokinase, phosphofructokinase, and pyruvate kinase. Glucose-6-phosphate and 6-phosphogluconate dehydrogenases were also markedly inhibited. Other enzymes of carbohydrate metabolism such as lactate dehydrogenase, phosphohexose isomerase, and fructose-1,6-diphosphatase were not decreased. Among the key glycolytic enzymes, the inhibition of pyruvate kinase by the fatty acid was most marked. The biological significance of the inhibition of the key glycolytic enzymes is interpreted as a feedback inhibitory mechanism in regulation of fatty acid biosynthesis. The mechanism may function for rapid adaptation by which the organism can use the fatty acid level as a metabolic directional switch in decreasing glycolysis and turning on gluconeogenesis.

Animals↗
PubMedDate not supplied

Regulation of macromolecular synthesis in Morris hepatomas.

In this review, some studies are discussed in which an attempt has been made to determine the nature of changes in macromolecular synthesis in Morris hepatomas. The incorporation of isotope labeled precursors into nucleic acids and proteins has suggested greatly increased rates of DNA synthesis in comparison with rat liver of normal and tumor bearing rats, but for RNA and proteins the changes may be impressive for individual macromolecular species but total synthesis is not greatly changed. Fractionation of nuclear proteins has indicated altered patterns of synthesis which are related to the growth rates of the tumors and are much more pronounced than in regenerating liver despite a growth rate similar to that of the most rapidly growing hepatomas. Investigations with drugs which inhibit synthesis of macromolecules has suggested that liver neoplasia may be accompanied by changes in response which may make the tumor less sensitive or more sensitive to regulation than the tissue of origin.

Amino Acids↗
PubMedDate not supplied

Metabolic limits on dive duration and swimming speed in the southern elephant seal Mirounga leonina.

The ability of air-breathing marine predators to forage successfully depends on their ability to remain submerged. This is in turn related to their total O(2) stores and the rate at which these stores are used up while submerged. Body size was positively related to dive duration in a sample of 34 adult female southern elephant seals from Macquarie Island. However, there was no relationship between body size and dive depth. This indicates that smaller seals, with smaller total O(2) stores, make shorter dives than larger individuals but operate at similar depths, resulting in less time being spent at depth. Nine adult female elephant seals were also equipped with velocity time depth recorders. In eight of these seals, a plot of swimming speed against dive duration revealed a cloud of points with a clear upper boundary. This boundary could be described using regression analysis and gave a significant negative relationship in most cases. These results indicate that metabolic rate varies with activity levels, as indicated by swimming speed, and that there are quantifiable limits to the distance that a seal can travel on a dive of a given swimming speed. However, the seals rarely dive to these physiological limits, and the majority of their dives are well within their aerobic capacity. Elephant seals therefore appear to dive in a way that ensures that they have a reserve of O(2) available.

Aerobiosis↗