The role of choline sulphate in the sulphur metabolism of fungi

Abstract

Choline sulphate synthesis in vitro by extracts of a number of fungi in the presence of adenosine triphosphate and Mg++ ions was shown to involve the intermediate formation of adenosine 3[image]-phosphate 5[image]-sulphatophosphate followed by the enzymic transfer of sulphate from this compound to choline. Adenosine 3[image]-sulphatophosphate could not act as a sulphate donor. All fungi tested produced adenosine 3[image]-phosphate 5[image]-sulphatophosphate in vitro but those fungi which did not accumulate choline sulphate in their mycelia in vivo could not transfer sulphate from adenosine 3[image]-phosphate 5[image]-sulphatophosphate to choline. The distribution of choline sulphate production can be discussed therefore in terms of the presence or absence of the transferase, choline sulphokinase. In competitive-metabolism experiments choline sulphate did not affect the utilization of SO4[long dash]by choline sulphate-less fungi without choline sulphate, including baker''s yeast. In the choline sulphate-producing fungi choline sulphate and SO4"" ions were competing sources of S for cysteine synthesis. Choline sulphate served as a good source of S for the growth of choline sulphate-producing fungi both in the absence and the presence of excess of Ba++ ions. Other sulphate esters, apart from chondroitin sulphate and 2:4-dichlorophenoxy-ethyl sulphate, were poor sources of S in the presence of Ba++ ions. Choline sulphate and nitrocatechol sulphate were good S sources for the growth of choline sulphate-less fungi both in the absence and the presence of Ba++ ions. When choline sulphate-producing fungi were grown on an adequate sulphur medium a store of choline sulphate accumulated in the mycelia which could be used to maintain further growth when the fungi were transferred to a medium totally deficient in S of any form. In the same circumstances no further growth of choline sulphate-less fungi occurred on the new S-deficient medium. Choline sulphate in fungal mycelia is envisaged as a store of easily assimilated sulphate existing in an activated state. The pathway of utilization is thought to involve transfer of sulphate from choline sulphate to adenosine 3[image]:5[image]-diphosphate with the formation of adenosine 3[image]-phosphate 5[image]-sulphatophosphate and the subsequent reduction of adenosine 3[image]-phosphate 5[image]-sulphatophosphate to give SO3[long dash]and eventually cysteine.