Mechanism of Sulphate Transfer from 4-Nitrophenylsulphate to Phenolic Acceptors via Liver Cytosolic Sulphotransferase

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Abstract
Phenol sulphotransferase from cat and rabbit liver cytosol has been investigated using 4-nitrophenylsulphate as primary sulphate donor. The first stage of the reaction involves sulphation of cofactor adenosine 3',5'-diphosphate to adenosine 3'-phosphate 5'- phosphosulphate, which in turn acts as sulphate donor for other phenolic acceptors. Adenosine 3',5'-diphosphate is regenerated in this second stage, so that the overall reaction is a sulphate transfer from 4-nitrophenylsulphate to the phenolic acceptor. High acceptor concentrations lead to inhibition of the reaction; very low concentrations give deviation from Michaelis-Menten kinetics. From the kinetic data, a mechanism is suggested in which an enzyme-adenosine 3'-phosphate 5'-phosphosulphate complex is formed in situ, with which the acceptor then interacts to give the final sulphate transfer. The system employed here is useful for the study of phenol sulphotransferase in view of the difficulty in obtaining adequate amounts of adenosine 3'-phosphate 5'-phosphosulphate from commercial sources.

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