Flavin nucleotides, glutathione reductase and assessment of riboflavin status.

The in vitro effects of flavin nucleotides on human erythrocyte glutathione reductase were studied. Flavin mononucleotide was found to be a potent inhibitor of glutathione reductase in haemolysates, having an effect at a concentration of 1 muM. Flavin adenine dinucleotide inhibited at a concentration at least ten fold this, lower levels producing the expected stimulation of enzyme activity. Different assay conditions also altered the activity of the enzyme, although the flavin mononucleotide inhibition remained. The implications of these findings in our understanding of glutatione reductase and in using the enzyme to assess riboflavin status are discussed.