Adenosine 5‘‐Phosphosulfate Sulfotransferase from Norway Spruce: Biochemical and Physiological Properties*

Abstract

AbstractBiochemical and physiological properties of adenosine 5′‐phosphosulfate sulfotransferase, a key enzyme of assimilatory sulfate reduction, from spruce trees growing under field conditions were studied. The apparent Km for adenosine 5′‐phosphosulfate (APS) was 29 ± 5.5μM, its apparent Mr was 115,000. 5′‐AMP inhibited the enzyme competitively with a Ki of 1 mM, but also stabilized it. MgS04 at 800 mM increased adenosine 5′‐phosphosulfate sulfotransferase activity by a factor of 3, concentrations higher than lOOOmM were inhibitory. Treatment of isolated shoots with nutrient solution containing 1 or 2 mM sulfate, and 3 or 10 mM glutathione, respectively, induced a significant decrease in extractable adenosine 5′‐phosphosulfate sulfotransferase activity over 24h, whereas GSH as well as S2‐ up to 5mM cysteine and up to 200 mM SO32‐ had no effect on the in vitro activity of the enzyme. As with other enzymes involved in assimilatory sulfate reduction, namely ATP sulfurylase (EC 2.7.7.4), sulfite reductase (EC 1.8.7.1) and O‐acetyl‐L.‐serine sulfhydrylase (EC 4.2.99.8), adenosine 5′‐phosphosulfate sulfotransferase was still detected at appreciable activities in 2‐ and 3‐year‐old needles. Adenosine 5′‐phosphosulfate sulfotransferase activity was low in buds and increased during shoot development, parallel to the chlorophyll content. The enzyme activity was characterized by an annual cycle of seasonal changes with an increase during February and March.