Distribution and properties of novel deglycating enzymes for fructosyl peptide in fungi

Abstract

Our fungal culture collection was screened for fructosyl peptide oxidase, an enzyme that could be used for the determination of glycated hemoglobin in diabetic subjects with hyperglycemia. Fructosyl peptide oxidases were found in strains of eight genera: Achaetomiella, Achaetomium, Chaetomium, Coniochaeta, Eupenicillium, Gelasinospora, Microascus and Thielavia. By their substrate specificity toward N ^α-fructosyl valyl-histidine (α-keto-amine) and N ^ε-fructosyl lysine (ε-keto-amine), fructosyl peptide oxidases could be categorized into two groups: (1) enzymes that oxidize both α-keto-amine and ε-keto-amine, and (2) enzymes that preferably oxidize α-keto-amine. A fructosyl peptide oxidase from Achaetomiella virescens ATCC 32393, active toward both N ^α-fructosyl valyl-histidine and N ^ε-fructosyl lysine, was purified to homogeneity and characterized. The enzyme was monomeric (M _r=50,000), was most active at 40 °C and pH 8.0, and had a covalently bound flavin as a prosthetic group. Apparent K _m values for N ^α-fructosyl valyl-histidine and N ^ε-fructosyl lysine were 2.30 and 1.69 mM, respectively. N ^α-fructosyl valyl-histidine was consumed and the same molar amount of valyl-histidine was produced by the fructosyl peptide oxidase reaction. This enzyme could be useful for the measurement of hemoglobin A_1C, the N-terminal valine residue of the β-subunit of which is glycated.