THIAMINASE ACTIVITY OF MYOGLOBIN OXOFERRYL FORMS

Abstract

Thiamine oxidation chemistry in presence of metmyoglobin and hydrogen peroxide is quite complex and different products can be formed. Incubation of thiamine with metmyoglobin and hydrogen peroxide can result in splitting of thiamine molecule at carbon atom of the methylene bridge and production of aminopyrimidine and thiazole components as separate molecules or in formation of thiochrome, thiamine disulfide, oxodihydrothiochrome, and thiaminethiazolone. Oxidative transformation of thiamine phosphate esters in presence of metmyoglobin and hydrogen peroxide gives similar products however thiaminase activity, i.e. splitting of the molecules into aminopyrimidine and thiazole phosphate parts, is much higher in this case. Addition of tyrosine or paracetamol to incubation mixture inhibits thiaminase activity and formation of disulfides, but yield of thiochrome or thiochrome phosphates increases. Identification of products of thiamine (or its phosphate esters) oxidation in the presence of metmyoglobin and hydrogen peroxide was performed using HPLC, mass-spectrometry and spectral-fluorescent methods. Role of oxoferryl forms of myoglobin in degradation of thiaminediphosphate, cofactor of the important enzymes of carbohydrate metabolism, by thiaminase mechanism is discussed.