Competitive inhibition between 4'-substituted pyridoxine analogues and pyridoxal for pyridoxal kinase from mouse brain.

4'-Substituted pyridoxine analogues (4'-PN analogues), which were potent antagonists of vitamin B6, induced severe convulsions in mouse which could be prevented by vitamin B6. To elucidate the mechanism of the convulsive action, the effect of 4'-PN analogues on partially purified pyridoxal kinase (PL-kinase) from mouse brain was studied. 4'-Methoxypyridoxine (4'-MPN), 4'-ethoxypyridoxine (4'-EPN), 4'-propoxypyridoxine (4'-PPN) and 4'-isopropoxypyridoxine (4'-isoPPN) were found to powerful inhibitors of PL-kinase and competed with pyridoxal (PL). There was a good relationship between mouse convulsions and inhibitory activities of PL-kinase. We also studied whether 4'-MPN, 4'-EPN, 4'-PPN and 4'-isoPPN were used as substrates of PL-kinase. High-performance liquid chromatography was used to separate 4'-PN 5'-phosphate analogues and ADP which were formed in the enzyme reaction, and to measure them quantitatively. The results showed that 4'-MPN, 4'-EPN, 4'-PPN and 4'-isoPPN were also phosphorylated by PL-kinase like 4'-deoxypyridoxine.