2,4,5-Trihydroxybutyrophenone (2,4,5-Thbp) as a Substrate for Horseradish Peroxidase

Abstract

2,4,5‐trihydroxybutyrophenone (2,4,5‐THBP), in the presence of hydrogen peroxide (H2O2), is a substrate for horseradish peroxidase (HRP) with a Km value of 2.5 mM. An intermediate red product(s), probably 2,4,5‐THBP quinone, characterized by a peak at 490–500 nm, was detected and the time course of its conversion to the final red product(s) was studied. The relationships between the rate of 2,4,5‐THBP oxidation to pigmented product(s) as a function of various concentrations of H2O2, 2,4,5‐THBP and HPR are described.

Effect of 2,3,4-Trihydroxyacetophenone (2,3,4-Thap) and 2,4,5-Trihydroxybutyrophenone (2,4,5-Thbp) on the Rate of Dl-Dopa Oxidation by Mushroom Tyrosinase

“…In the course of our study to explain the ability of gallic acid, 4-methyl gallate, n-propyl gallate, 2,3,4-THAP and 2,4,5-THBP to prevent DL-DOPA conversion to melanin via tyrosinase, we noted that 2,3,4-THAP and 2,4,5-THBP, each stimulated the rate of DL-DOPA oxidation to dopachrome, this being surprising since 2,3,4-THAP and 2,4,5-THBP are substrates for mushroom tyrosinase (Kahn 1990b;Kahn et al 1991).…”

“…1991). The rate of oxidation of 2,4,5-THBP by mushroom tyrosinase to material absorbing at 480-500 nm was high initially and then decreased with time, suggesting that the initial intermediate product (2,4,5-THBPquinone) (h = 510 nm) is converted to a colorless polymerized 2,4,5-THBP-OH, which is further oxidized nonenzymatically to the final product, a red polymerized 2,4,5-THBPquinone (A = 490 nm) (Kahn et al 1991).…”

“…It was surprising that 2,3,4-THAP and 2,4,5-THBP, which are substrates for tyrosinase (Kahn 1990;Kahn et al 1991), did not inhibit the rate of DL-DOPA oxidation by tyrosinase but rather stimulated the reaction. It was therefore important to establish whether the stimulation exerted by 2,3,4-THAP on the rate of DL-DOPA oxidation by tyrosinase ( Fig.…”

“…The finding that 2,3,4-THAP and 2,4,5-THBP prevented the conversion of DL-DOPA to DOPA-melanin via tyrosinase is probably due to the higher affinity of the enzyme to DL-DOPA than to these trihydroxyphenols so that more dopaquinone was formed and enough trihydroxyphenol was still present during the 20 h incubation period to couple with the dopaquinone formed. h d d , tyrosinase has a higher apparent affinity to DL-DOPA than to 2,3,4-THAP or to 2,4,5-THBP as judged by the fact that the Km of DL-DOPA to the enzyme is 0.48 mM (Kahn et al 1991), that of 2,3,4-THAP is 1.2 mM (Kahn 1990) and that of 2,4,5-THBP is 1.0 mM (Kahn et al 1991).…”

EFFECT OF BENZENESULFINIC ACID ON THE OXIDATION OF o-DIHYDROXY - AND TRIHYDROXYPHENOLS BY MUSHROOM TYROSINASE

“…Oxidation of 2,4,5 THBP by tyrosinase yields initially the corresponding o-quinone (Amm = 500k10 nrn). The red 2,4,5 THBP-o-quinone is converted to a colorless polymerized 2,4,5 THBP-OH which is then oxidized to a final red polymerized 2,4,5 THBP-o-quinone (Kahn et al 1991).…”