Regulation of the O-acetyl-L-serine(thiol)lyase activity in Monoraphidium braunii

Total level of O-acetyl-L-serine(thiol)lyase (OASTL) activity observed in M onoraphidium braunii fed-repleted cells decreases up to 40 % after 24 h the carbon source was removed from the culture; however no significant change in the activity is observed in N-starved cells. On the other hand, sulfur s tarvation induces OASTL activity in M, braunii, which may increase 2.5-fold after 36 h. Normal intracellular level of the activity is restored when a sulfur source, such as sulfate, sulfite, L-cysteine, L-methionine or glutat hione is added to the culture. The induction of the OASTL activity requires de novo synthesis of protein, and thus the presence in the culture of adeq uate carbon and nitrogen sources. The OASTL isoenzymes from M. braunii cell s are differently affected by S-starvation.