Regulation of factors that influence the in vitro stability of tryptophan synthetase from yeast.

The activity of tryptophan synthetase in crude extracts from Saccharomyces cerevisiae is stable if the cells are cultured in a complex medium, but extremely unstable if they are cultured in a minimal medium. The difference is not the result of different inherent properties of the enzyme formed in the two cultures. Rather, there are at least two kinds of macromolecular factors that influence the stability, one inactivating tryptophan synthetase and the other protecting against this inactivation. The abundance of these factors varies with the composition of the culture medium, which accounts for the differences observed.