Cellular location of asparaginase activity in Saccharomyces cerevisiae and regulation of this activity by nitrogen compounds.

Three asparaginase activities have been detected in Saccharomyces cerevisiae. One is found outside the permeability barrier; a second one is found inside and is soluble in the cell, and the third one is localized in a system of membrane particles. Synthesis of the membrane and external asparaginases require "de novo" synthesis of RNA and protein. The synthesis of exocellular asparaginase is inhibited by several nitrogen compounds (catabolite repression). This inhibition might take place at the transcriptional level. Moreover, this isoenzyme is reversibly inactivated by its natural substrates (catabolite inhibition by substrates). The half life of external asparaginase mRNA was calculated by two independent methods and values of 7.5 and 9.5 min were found.