Abstract
Seven pyridine nucleotide analogs were synthesized, including nicotinic acid mononu-cleotide, nicotinic acid-adenine dinucleotide, and nicotinic acid-adenine dinucleotidephos-phate, by means of the transglycosidase activity of rabbit spleen pyridine nucleotide glycohydrolase. The velocity ratio of the transglycosidation to the hydrolysis in the pres-ence of 16mM nicotinamide mononucleotide and 0.3M nicotinic acid at pH 5.2 was greater than 10 and the transglycosidation/hydrolysis partition ratio was estimated to be (12±2)×103. The partition ratio values obtained with 3-acetylpyridine and nicotinylglycine were smaller than that with nicotinic acid. Configurational analysis of pyridinium C-N glycosidic linkages of the transglycosidation products by means of 1H-NMR, UV, CD, and paper chromatography indicated that the configuration was completely retained and absolutely β. Retention of the configuration, together with the substrate specificity of the enzyme for the β-pyridinium linkage and formation of the intermediary enzyme-phosphoribosyl (or ADP-ribosyl) complex during the enzyme catalysis, indicated that the transglycosidation reaction catalyzed by the enzyme proceeds through the double replacement mechanism.
