Regulation of Enzyme Activity in Ontogenesis

3) Regulation of enzyme activity in ontogenesis. Many mechanisms exist in biological systems for the activation and inhibition of activity of enzymes and enzyme cycles, for enzyme function is the most labile and dynamic component of the living system enabling constant adaptation to constantly changing 

Enzyme activity is controlled by changes in the conformation of the molecules, masking and unmasking of the active centers, the relative proportions of isozymes, substrate concentration, concentration of the end product, activators and inhibitors at the genetic level, activators and inhibitors at the functional level, hormones, coenzymes, fluctuations in pH and ionic strength of the medium, and many other factors. Of these other factors the most important are the velocity of synthesis and breakdown of enzymes, determining the enzyme concentration in the cytoplasm and other media of the organism. 

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. 

Many factors which influence enzyme activity at this period, such as embryonic hormones, inducers, and so on, do so in fact through their action on the DNA RNA enzyme chain, i.e., through activation of a particular gene. In normal morphogenesis this type of activation and repression can thus be regarded as elements of the strict program of development. 

These facts, and all the material we have previously examined on ontogenetic changes in the protein and enzyme spectrum, make it clear that the key to the understanding of the programming of biochemical development lies at the level of DNA-dependent genetic) RNA synthesis. 

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