Mechanism of Choline Sulphate Utilization in Fungi

Abstract

CHOLINE sulphate is synthesized by higher fungi¹, algae² and plants³. In fungi it is found in high concentration in the mycelium⁴ and in spores⁵ and is thought to act as a store of sulphur^6,7 and possibly carbon and nitrogen. Synthesis of choline sulphate^6,8 involves activation of inorganic sulphate by the enzymes ATP-sulphate adenylyltransferase (EC.2.7.7.4), (ATP-sulphurylase)and ATP-adenylyl 3′-phosphotransferase (EC.2.7.1.25), (APS-kinase), to give adenosine 3′-phosphate 5′-sulphatophosphate (PAPS) and the subsequent transfer of the sulphate group of PAPS to choline catalysed by 3′-phosphoadenylylsulphate: choline sulphotransferase (EC. 2.8.2) (choline sulphotransferase)⁹. The mechanism of the utilization of the sulphur of choline sulphate for cysteine synthesis has been in some doubt. A reversal of the choline sulphotransferase reaction to give PAPS which could then be converted to SO₃²⁻ and then to cysteine has been ruled out^9,10. Several workers have failed to detect a choline sulphatase in fungi^11,12, and while this enzyme has been detected in A. sydowi and P. chrysogenum¹³, the activity of the enzyme was very low and its physiological significance uncertain. Evidence is now presented confirming the presence of choline sulphatase in fungi and establishing that this enzyme is obligatory for choline sulphate utilization.