Biochemistry of sheep tissues. Enzyme systems of liver, brain and kidney.

Little information is available on the enzyme activities of sheep tissues in vitro. Kleiber (1941, 1947) measured the oxygen consumption of liver slices of rats, rabbits and sheep, and attempted to correlate the QO, of this tissue with the metabolic rate of the living animal and to establish a direct relationship to body size. However, Krebs (1950), using more refined and standardized techniques, has shown that, although the QO, values of the tissues of larger animals are lower than the corresponding values for smaller species, there is no direct relationship to the basal heat production of the intact aninal. The QO value for most tissues changes much less with body weight than does the rate of heat production. Krebs attributed the differences in basal heat production in animals of different size mainly to variation in the QO of muscle, and suggests that the metabolic rate of other tissues is govemed by the specific energy requirements of the particular tissue and not by the heat requirements of the whole body. Comparative Qo3 values from various tissues and species, including sheep, are published by Krebs (1950) and Albritton (1954). These figures are of general interest but cannot supply information on the activities of isolated enzyme systems. More specific data are available on the metabolism of shortchain fatty acids by sheep-rumen epithelium and slices of kidney and liver (Pennington, 1952, 1954; Annison &; Pennington, 1954; Pennington & Sutherland, 1954, 1955, 1956a), ketone-body production from certain substrates by rumen epithelium (Pennington & Sutherland, 1956b) and the metabolism of acetate and glucose by sheep mammary-gland slices, particularly in relation to lipogenesis (Folley & French, 1950; Balmain, Folley & Glascock, 1952, 1954; Duncombe & Glascock, 1953, 1956). The aims of the present study were: to measure the activity of enzyme systems of sheep liver, brain and kidney; to observe where and how the metabolic pattern differs from that of other species; to note variations which might be attributable to