Hydrolytic Activity of α-Mannosidase against Deoxy Derivatives of p-Nitrophenyl α-D-Mannopyranoside

Abstract

Deoxy derivatives of p-nitrophenyl (PNP) α-D-mannopyranoside, PNP 2-deoxy-α-D-arabino-hexopyranoside, 3-deoxy-α-D-arabino-hexopyranoside, 4-deoxy-α-D-lyxo-hexopyranoside, and α-D-rhamno-pyranoside, were synthesized and hydrolytic activities of jack bean and almond α-mannosidases against them were investigated. These α-mannosidases scarcely acted on the 2-, 3-, and 4-deoxy derivatives, while the 6-deoxy one was hydrolyzed by the enzymes as fast as PNP α-D-mannopyranoside, which is a common substrate for α-mannosidase. These results indicate that the hydroxyl groups at C-2, 3, and 4 of the mannopyranoside are necessary to be recognized as a substrate by these enzymes, while that at C-6 does not have so a crucial role in substrate discrimination. Values of K_m and V_max of the enzymes on the hydrolysis of PNP α-D-rhamnopyranoside were obtained from kinetic studies.