Abstract
Two hydroxylation reactions of m‐cresol, an intermediate in the secondary biosynthesis of the antibiotic patulin, have been characterised in cell‐free preparations of Penicillium patulum. The ability to convert m‐cresol to 2,5‐dihydroxytoluene and m‐hydroxybenzyl alcohol is located in separable fractions of the 105000 × g microsomal pellet. The activities had Km values for m‐cresol of 80 μM and 5 μM, respectively. Both reactions require molecular oxygen and NADPH for activity. Inhibition of m‐cresol hydroxylases by carbon monoxide is reversible by light with a photochemical action spectrum maximal at 450 nm. Carbon monoxide difference spectra of mycel extracts show the presence of absorbing pigments at 422 and 450–455 nm.The enzymes are not appreciably inhibited by cyanide but are inhibited by cytochrome c. m‐Cresol hydroxylation therefore appears to be catalysed by typical mixed‐function oxidases involving an NADPH‐dependent reductase and a pigment like cytochrome P‐450.In the light of studies on the utilisation of radioactively labelled intermediates, the methyl hydroxylation of m‐cresol to m‐hydroxybenzyl alcohol probably represents an important reaction in the sequence leading to patulin formation. Ring hydroxylation of m‐cresol to 2,5‐dihydroxytoluene appears to be a side reaction functional at higher concentrations of m‐cresol.
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