The activities of some enzymes concerned with energy metabolism in mammalian muscles of differing pigmentation

Abstract

1. Extractable hexokinase activity was measured in the red and white skeletal muscles of the rabbit and in the hearts and diaphragms of four animal species differing markedly in size. Activities vary over a 40-fold range, being least in white skeletal muscle of the laboratory rabbit and greatest in mouse heart. 2. Hexokinase activities correlate approximately with capacities to undertake reactions of the tricarboxylic acid cycle as determined by succinate oxidase assays. Both enzyme activities seem best related to the average contractile-energy expenditure per unit weight of muscle over an extended period, rather than to the rapidity of individual contractions. 3. Hexokinase and succinate oxidase activities cannot be related to a muscle's content of soluble pigment. They display an inverse relationship with activities of phosphorylase and glycolytic enzymes, but only within the group of rabbit skeletal muscles whose oxidative capacities are at the lower end of the observed range. 4. Total glycogen-UDP glucosyltransferase activities do not vary significantly between rabbit skeletal muscles, although those of hexokinase differ by about sixfold. On the average, glucose 6-phosphate is probably oxidized directly. However, observations cited in the literature suggest that muscles with an active hexokinase may well preferentially accumulate glycogen when glucose is present in excess of the fibres' capacity to oxidize it. 5. When considered with published results obtained in vivo, the present findings indicate that phosphorylase has a minor role in the energy expenditure of muscles with a predominantly oxidative metabolism. In these, the major substrates appear to be blood glucose, fatty acids and possibly lipids. 6. The histochemical criteria by which muscle fibres are commonly described as red or white are inadequate.

A comparative study of glycolysis in red and white muscles of the trout (Salmo gairdneri) and mirror carp (Cyprinus carpio)

“…Thus the hexokinase activities of vertebrate twitch muscles have been shown to be 2-10 times higher in red than white muscles (Burleigh & Schimke, 1969;Crabtree & Newsholme, 1972). Similar findings have been obtained for both fish species in the present study.…”

Glycogen synthetase in developing and adult skeletal muscle

“…Here we report results that confirm and extend the observations made by Burleigh & Schimke (1969), by showing that total synthetase activity is largely independent of the metabolic and functional properties of individual muscles from various species. Further, the postnatal development of the synthetase was investigated in rat skeletal muscle and contrasted with that of glycogen phosphorylase (EC 2.4.1.1).…”

“…These metabolic differences were correlated with the relatively higher activity of total (I+D) synthetase in the red, aerobically oriented, fibres in the rat and the monkey (Bocek & Beatty, 1966) and in the guinea pig (Stubbs & Blanchaer, 1965). On the other hand Burleigh & Schimke (1969) were unable to find significant differences in the total synthetase activity/unit fresh tissue weight of several muscles of the rabbit.…”

Thyroid Hormone Induced Changes in the Enzyme Activity Pattern of Energy‐Supplying Metabolism of Fast (Whit) Slow (Red), and Heart Muscle of the Rat

“…The homogenate was brought t o 1 0 m l and a n aliquot ( 2 ml) was shaken for 30 min with lo/, Triton-X-100 t o free the bound hexokinase [14]. This sample was then centrifuged for 20 min at 244000 x g and the supernatant used for hexokinase determination.…”

“…As was shown in previous communications (for references see [i l]), marked differences exist between the enzyme activity patterns of energy-supplying metabolism in white and red muscle. It wits therefore the purpose of this study to compare muscles of different metabolic type (white, red and heart muscle [11][12][13][14][15][16]) with regard to their response to increased levels of thyroid hormones. Activities of enzymes were examined which in previous studies had been shown to represent definite metabolic systems and to indicate by their ratios certain metabolic correlations.…”