Abstract
α^4-Norpyridoxine 5'-phosphate (4-NOP-P) was synthesized and its antivitamin B_6 activity in vitamin B_6 apo-enzyme systems was tested. 4-NOP-P as well as 4-deoxypyridoxine 5'-phosphate (4-DOP-P), showed a competitive inhibition against pyridoxal 5'-phosphate in the reaction systems using aspartate aminotransferase from baker's yeast and tyrosine aminotransferase from rat liver (K_i=0.45×10^<-7>M and 0.7×10^<-7>M, respectively). 4-NOP-P exerted a noncompetitive inhibition (K_i=3.7×10^<-6>M) on tryptophanase from Escherichia coli, while 4-DOP-P showed no inhibition. α^4-Norpyridoxine exerted no effect on pyridoxine dehydrogenase from baker's yeast.
