The tyrosinase-tyrosine reaction

Comparative Biochemistry of the Phenolase Complex

“…The enzymic formation of melanin from 3,kdihydroxyphenylalariine may require about 4.6 atoms of oxygen per molecule, the consumption rising with pH and with buffer concentration a t any given pH (53,461). This corresponds to 1.6 atoms of oxygen/molecule of indole-5,6-quinone polymerized, theoretically 1 .O atom.…”

Synthesis of the Indole Nucleus

“…The aminochrome obtained from the enzymatic oxidation of N-methyltyrosine, treated in aqueous solution with sulfur dioxide, gave 5,6-dihydroxy-l-methylindole-2-carboxylic acid isolated as the dimethyl ether. 513 Similarly, an aqueous solution of epinochrome (688) containing sulfur dioxide gave 5,6-dihydroxy-1-methylindole, also isolated as its dimethyl ether. 513 It is known that reducing agents do promote the conversion of aminochromes to indoles, and accordingly it has been considered that this is the property of sulfur dioxide that causes the conversion of aminochromes to indoles.s62e 571 However, this is by no means certain and has been questioned.5s2 It may well be that it is the sulfurous acid that is responsible for the observed enhanced rate of conversion.…”

“…513 Similarly, an aqueous solution of epinochrome (688) containing sulfur dioxide gave 5,6-dihydroxy-1-methylindole, also isolated as its dimethyl ether. 513 It is known that reducing agents do promote the conversion of aminochromes to indoles, and accordingly it has been considered that this is the property of sulfur dioxide that causes the conversion of aminochromes to indoles.s62e 571 However, this is by no means certain and has been questioned.5s2 It may well be that it is the sulfurous acid that is responsible for the observed enhanced rate of conversion. Indeed, the presence of the acid would account for the preferential retention of the carboxylic acid group as well as the accelerated rate of rearrangement by maintaining the protons on both the carboxyl group and the ring nitrogen.…”

The Biogenesis of Alkaloids: Xvi. Hordenine Metabolism in Barley

“…Investigations of the behavior of hordenine toward isolated enzymes have shown that whereas tyrosine is converted by tyrosinase to melanin (4,9,19) hordenine is not, because of the substitution on the nitrogen. The product of the oxidatioil of hordenine by a preparatioil from Scotch broom containing tyrosinase has beell identified as o-hydroxyhordenine (3).…”