A sulfotransferase from spinach leaves using adenosine-5'-phosphosulfate.

Active sulfotransferase can be extracted from spinach (Spinacea oleracea L.) leaves (and other higher plants) using a buffer system containing 0.1 M KCl and thiol reagents. This sulfotransferase is labile, it can, however, be stabilized by storage in 70% ammonium sulfate containing 10 mM mercaptoethanol. This extract will reduce labelled adenosine-5'-phosphosulfate (APS) and 3'-phosphoadenosine-5'-phosphosulfate (PAPS) to acid-volatile radioactivity when dithioerythrol is added. The reduction from PAPS requires magnesium chloride and is inhibited by calcium chloride and sodium fluoride, whereas these chemicals have little effect on the APS-sulfotransferase activity. The reduction rates from both nucleotides are stimulated by increasing ionic strength and are inhibited by phosphate and cyanide. In the presence of non-labelled APS the acid-volatile radioactivity distilled from [(35)S] PAPS is drastically reduced, whereas the opposite experiment using [(35)S] APS in the presence of non-labelled PAPS has little effect. This indicates that APS is an obligatory intermediate in the conversion of [(35)S] PAPS to acid-volatile radioactivity. It is therefore concluded that the sulfotransferase from spinach is specific for APS. Activity with APS as sulfur-donor was found in 5 other plants in addition to spinach: Pennisetum, Zea (Gramineae); Brassica (Cruciferae); Helianthus (Compositae); and Vicia (Papilionaceae). These experiments demonstrate the use of APS for assimilatory sulfate reduction in higher plants. This has been shown previously for the green alga Chlorella.