A comparison of the kinetic and other parameters of enzymes of flavin-nucleotide metabolism in the whole foetus vis-à-vis the maternal liver in the pregnant rat revealed relatively lower activities of foetal flavokinase and FAD pyrophosphorylase. Passive immunoneutralization of the maternal riboflavin carrier protein suppresses foetal FAD pyrophosphorylase rather selectively. Additionally, although the activities of foetal nucleotide pyrophosphatase and FMN phosphatase were unchanged owing to immunoneutralization, higher activities of these enzymes in the whole foetus as compared with the maternal liver may be responsible for the drastic depletion of FAD levels that precipitates foetal degeneration.

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