Analysis of the regulation of adenosine 5′-phosphosulfate sulfotransferase activity in Lemna minor L. using 15N-density labeling

The role of de novo synthesis in the regulation of adenosine 5′-phosphosulfate sulfotransferase activity by H2S inLemna minor L. was investigate using density labeling with15N applied as15NO 3 − in the culture medium. While adenosine 5′-phosphosulfate sulfotransferase activity was rapidly reduced by H2S and rapidly recovered upon removal of H2S, O-acetyl-L-serine sulfhydrylase (EC 4.2.99.8) did not show changes in extractable activity in response to H2S and could therefore be used as an internal marker enzyme for density labeling. The incorporation of15N into adenosine 5′-phosphosulfate sulfotransferase was strongly reduced upon transfer of plants into a H2S-containing atmosphere. Half-maximal labeling was reached only after 70–80 h compared to 40–50 h in the control. After removal of H2S, adenosine 5′-phosphosulfate sulfotransferase activity increased to the initial level within 20 h, and the enzyme reached halfmaximal labeling after only 15 h. The time course of the density increase of O-acetyl-L-serine sulfhydrylase was not affected very significantly by H2S. These results provide evidence that de novo synthesis of enzyme protein is involved in the regulation of adenosine 5′-phosphosulfate sulfotransferase activity by H2S