Vitamin B
6 functions primarily as pyridoxal 5′-phosphate (PLP) in body processes. PLP is the coenzyme of various enzymes involved in the metabolism of nitrogen-containing molecules, namely amino acids. PLP can catalyze a variety of reactions such as transamination, decarboxylation, elimination, replacement, and aldol condensation/cleavage. However, in the presence of enzyme proteins, PLP catalyzes a specific type of reaction and simultaneously enhances its catalytic efficiency. Analyses on the interactions between PLP and enzyme proteins are, therefore, of great importance for understanding the function of vitamin B
6 enzymes. Aspartate aminotransferase imposes strain on the Schiff base between PLP and the active site Lys and increases the energy level of E + S, thereby enhancing
kcat/
Km by 10
3 folds. In threonine synthase, the phosphate ion released from the substrate
O-phospho-L-homoserine remains at the active site and directs the reaction to catalyze the β-elimination/γ-addition reaction. Knowledge on the reaction specificity of decarboxylases is also important for elucidating the physiological functions of these enzymes in mammalian cells.
抄録全体を表示