Based on the specific activities in rat and human liver
cytosol, it could be estimated that per milligram of protein this
enzyme activity in human cytosol was only 0.8% of the activity
measured in rat cytosol. Edwards et al. (20) have studied DTdiaphorase
in water extracts of various human tissues. Their
data are consistent with the relatively low concentration of the
enzyme we have measured in human liver. Thus, it appears that
the warfarin-sensitive DT-diaphorase in human liver plays only
a minor role in the dehydrogenase pathway for vitamin K, reduction.
In support of this assumption is our data on the effect
of warfarin on [NADH + vitamin K1]-supported carboxylase
activity. High concentrations of warfarin had no significant effect
on this activity. In addition, these data present evidence for the
existence of a warfarin-insensitive dehydrogenase in human liver