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Activity patterns of key enzymes in energy‐supplying metabolism were studied in a typical fast (white) muscle ( pars posterior of m. latissimus dorsi ) and in a typical slow (red) muscle ( pars anterior of m. latissimus dorsi ) of the chicken during postnatal development. The differentiation of these enzyme activity patterns occurs postnatally, and is practically completed after 3 weeks. After hatching, the enzyme activity patterns of the two muscles resemble each other, and correspond to that of a slow muscle, with predominantly aerobic metabolism. The slow muscle does not change its metabolic type markedly during development. The postnatal differentiation of the fast muscle, however, implies a pronounced change of its metabolic type. It consists of a parallel increase of absolute and specific activities of enzymes representing the following metabolic systems: glycogenolysis (glycogen phosphorylase), glycolysis (triosephosphate dehydrogenase), lactic fermentation (lactate dehydrogenase), and glycerolphosphate metabolism (glycerol‐3‐phosphate dehydrogenase). These concomitant changes suggest a coordinate synthesis of the respective enzymes. This conclusion applies also to a second group of enzymes which, however, decrease in absolute and specific activities. This group consists of enzymes representing the citric‐acid cycle (citrate synthase), fatty‐acid oxidation (3‐hydroxyacyl‐CoA dehydrogenase) and glucose phosphophorylation (hexokinase). Thus, enzymes belonging to constant proportion groups change in parallel during postnatal development of the muscle, and metabolic differentiation is reflected mainly by inverse shifts of constant proportion enzyme groups representing aerobic and anaerobic systems of energy‐supplying metabolism.
Bass et al. (Wed,) studied this question.