The activities and intracellular distributions of enzymes of carbohydrate, lipid and ketone-body metabolism in lactating mammary glands from ruminants and non-ruminants

Abstract

1. The activities of several enzymes of carbohydrate, lipid, acetate and ketone-body metabolism were measured in lactating mammary glands from rats, mice, rabbits, guinea pigs, sows, sheep, cows and goats. The intracellular distributions of many of the enzymes were measured by fractional extraction. 2. Acetyl-CoA synthetase was predominantly cytoplasmic in rats and guinea pigs, but was more mitochondrial in the other species. The different location of this enzyme in rats and mice is discussed in relation to the disposal of reducing equivalents. 3. 3-Oxo acid CoA-transferase and acetoacetyl-CoA thiolase assayed at 600 microM-CoA were predominantly mitochondrial in all species investigated. Acetoacetyl-CoA thiolase assayed at 8 microM-CoA was predominantly cytoplasmic, except in rabbits and guinea pigs. Ruminants appeared to possess little, if any, of the cytoplasmic enzyme. 4. The activities and distributions of NADP-isocitrate dehydrogenase were consistent with a role in supplying cytoplasmic NADPH in ruminant tissue, and indicated that this system may also occur in guinea pigs.

Physiology and Biochemistry of Lactation

“…The other product of this cycle, glyceraldehyde phosphate, re-enters the glycolytic pathway in the case of the rat. In the ruminant, however, in which appreciable levels of the gluconeogenic enzyme fructose bisphosphatase occur, it is probably recycled to hexose phosphate in order to conserve carbohydrate (Crabtree et al, 1981). In those species where sialyllactose is a significant milk sugar, glucose also provides the N-acetylglucosamine from which the sialyl moiety is synthesized.…”

Evidence that the production of acetate in rat hepatocytes is a predominantly cytoplasmic process

“…Reagents, enzymes and radioactive compounds were obtained from the sources given previously (Crabtree et al, 1981(Crabtree et al, , 1987, except for the following: collagenase and bovine serum albumin (fatty acid-free) were obtained from Boehringer Corp., Lewes, East Sussex, U.K; Lcarnitine, sodium butyrate and oleic acid were from Sigma, Poole, Dorset, U.K.; (-)-hydroxycitrate was a gift from Dr. P. F. Sorter, Hoffmann-La Roche, Nutley, NJ, U.S.A. Oleic acid was added to incubations as a complex with defatted albumin, prepared as described by Snoswell et al (1982).…”

Impact of lean growth genotype, dietary amino acid regimen and level of chronic immune system activation on sow lactational performance

“…Stearate, oleate, and palmitate contribute less than 2% of the carbon dioxide produced in the lactating goat (Annisson et al, 1967) and lactating manmiary tissue of rats and mice in vitro (Rao and Abraham, 1975;Robinson and Williamson, 1978). Only in starvation does fatty acid oxidation supply significant ATP for mammary metabolism even though a high capacity for fatty acid oxidation exists in the mammary glands of many species (Crabtree et al, 1981).…”