Effects of Hormones and Nutrients

The effect of nutrients in inhibiting protein breakdown is most noticeable on proteins of long half-life (Poole and Wibo, 1973 Knowles and Ballard, 1976) and is not seen at all with very unstable proteins. Whereas comparable studies have not been performed using enzymes with a range of half-lives, it is reasonable to expect that general effects of nutrients would follow such a pattern and preferentially affect enzymes with long half-lives. 

Serum addition to hepatoma cells maintained in serum-free medium initiates cell growth and division and produces a transient but 

Although insulin decreases protein breakdown in cultured cells, it has no effect on the degradation rate constants of two enzymes with short half-lives, phosphoenolpyruvate carboxykinase (Gunn et al., 1976) and tyrosine aminotransferase (Reel et al., 1970). This negative result is in keeping with the concept that insulin acts by reducing auto-phagy, a process that seems trivial in the breakdown of proteins with short half-lives (Knowles and Ballard, 1976). 

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