“Vitamin … by warfarin … pyridoxal-5-phosphate (PAL-P) inhibited the activity, especially when microsomes were preincubated with PAL-P. The enzyme activity was not inhibited by N-methyltetrazolethiol (…, suggesting that the hypoprothrombinemia caused by beta-lactam antibiotics was not due to the inhibition of NADH-dependent vitamin K reductase.”