Enzyme activities, during embryonic development

The tissue distribution of adenine phosphoribosyltransferase varies considerably in rat, mouse, man, and monkey, and representative data are shown in Table 8-1. Murray 30) has found that the kinetic parameters of this enzyme in mouse liver vary during the course of embryonic development and has suggested that two forms of the enzyme may appear in succession. Both Murray 30) and Epstein 31) have observed marked changes in adenine phosphoribosyltransferase activity during embryonic development. 

The level of activity of enzyme synthesis and, consequently, the level of activity of the corresponding genes are mainly responsible for determining the changes in enzyme systems during embryonic development which we have just examined. 

Enzymes with an initially low activity which gradually increased during embryonic development. To this group of enzymes belong fructose-1,6-diphosphate aldolase (FDP-aldolase) and NAD-dependent malate dehydrogenase (NAD-MDH). The activities of these enzymes increased gradually until the morula-blastocyst transition, whereupon the enzyme activity increased more rapidly (Epstein et al., 1969). 

Another typical example of individual behavior of enzymes during embryonic development is shown in Fig. 78, demonstrating the dynamics of activity of four enzymes in the first week of development of the chick embryo (Moog, 1965). 

The mitochondria of embryonic cells are often found to be morphologically less complex than those of mature tissues. During development, changes occur in the size, shape, and arrangement of cristae as corollaries to changes in content and activity of enzymes and in respiratory and phosphorylative activity. 

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