Sulphation of p-hydroxyphenylpyruvic acid and related compounds by the rat liver cytosol

Cytosol preparations of rat liver and kidney were examined for their ability to transfer sulphate from adenosine 3′-phosphate 5′-sulphatophosphate to p-hydroxyphenylpyruvic acid. Little activity towards this substrate was observed, and the main product detected in the reaction mixtures was identified as p-hydroxybenzyl alcohol O-sulphate. This was not formed from p-hydroxybenzaldehyde, a spontaneous oxidation product of p-hydroxyphenylpyruvic acid, by sulphation followed by a rapid enzyme-catalysed reduction of the intermediate phydroxybenzaldehyde O-sulphate. This product was formed mainly by this sequence of reactions, but the reverse, reduction followed by sulphation, also appeared possible. p-Hydroxybenzyl alcohol itself was very readily sulphated by both preparations, and the liver also produced a sulpho-conjugate of homogentisic acid. These observations are important in calculating the turnover of L-tyrosine O-sulphate in the mammalian system, and establish that p-hydroxyphenylpyruvic acid O-sulphate is an end product of its metabolism, rather than an intermediate in its synthesis by reversed transamination.