Regulation of enzymes of assimilatory sulfate reduction in aerated cell suspension cultures of Nicotiana sylvestris

Abstract

The regulation of ATP sulfurylase (EC 2.7.7.4), adenosine 5′-phosphosulfate sulfotransferase (APSSTase) and O-acetyl-L-serine sulfhydrylase (OASSase, EC 4.2.99.8) by H 2S and cysteine in aerated cell suspension cultures of Nicotiana sylvestris was investigated. Aeration with 6 μl · 1 −1 H 2S or addition of 0.1 mM cysteine to the culture medium did not affect significantly ATP sulfurylase and OASSase activity or the doubling time of the cells, but caused a rapid decrease in extractable APSSTase activity. Parallel to the decrease in APSSTase activity in H 2S treated cells there was an increase in the cysteine content of the cells. Both effects were readily reversible after omission of H 2S. The uptake and the reduction of radioactive sulfate were inhibited in cells containing low APSSTase activity.