Adenosine Triphosphate Sulfurylase and O-Acetylserin Sulfhydrylase in Photoheterotropically and Heterotrophically Cultured Tobacco Cells

Abstract

Abstract Photoheterotrophic and heterotrophic cell suspension cultures of Nicotiana tabacum have been examined for changes in specific activity of ATP-sulfurylase (EC 2.1.1 A) and OAS-sulfhydrylase (EC 4.2.99.8) during growth on different nitrogen sources. During exponential growth the specific activity of ATP-sulfurylase and OAS-sulfhydrylase remained constant and was on the same level in cells with high and with low rates of sulfate assimilation. The specific activity of both enzymes rapidly increased in green photoheterotrophic cells as well as in chloroplast-free heterotrophic cells after the sulfur from the medium had been used up. This increase was reversed when the cells were transfered back to a sulfate supplemented nutrient solution. The changes in enzyme activity due to sulfur depletion seem to indicate a regulatory mechanism for these enzymes.