Abstract
The enzymatic property of pyridoxaminephosphate oxidase (EC 1.4.3.5: pyridoxarninephosphate: oxygen oxidoreductase (deaminating)) purified from various sources so far, was compared with each other. It was discussed whether the enzyme could utilize PMP or PNP as the true substrate in the PLP production in vivo. A11 the enzymes could oxidyze two naturally occurring vitamin B6 derivatives, PMP and PNP, but the relative activity for PNP to PMP, was considerably different from origin to origin. The enzyme purified from baker's yeast was the most specific one for PMP so far investigated. The ratio of PNP oxidase to PMP oxidase at 285 μM substrate concentration was about 0.25:1 in 0.2 M Tris-HCI buffer (pH 8.0). However, the ratio was altered to about I . I : I in 0.2 M Hepes-KOH buffer (pH 8.0) after the enzyme preparation was dialyzed against the same buffer. The pyridoxinephosphate oxidase activity found in wheat seedlings was separated into two fractions when the crude, acid-treated preparation was subjected to a DEAE-Sephadex A-50 column. These two fractions, suggesting to be isozymes, were significantly different from each other in enzymatic property as well as in the mobility on electrophoresis. One fraction was considerably specific for PNP, being associated with only about 10% of its activity for PMP.
