Involvement of lysine residue in the nucleotide binding of pigeon liver malic enzyme: modification with affinity label periodate-oxidized NADP.

1. Periodate-oxidized NADP, a competitive inhibitor of malic enzyme with respect to NADP, inactivate the enzyme in mild conditions. 2. The inactivation is due to the modification of an essential lysine residue. 3. Two molecules of reagent were found to be incorporated into the enzyme tetramer after extensive modification. 4. Complete protection of malic enzyme from the oxidized NADP inactivation was afforded by NADP and its analogues. 5. The modified enzyme showed increased apparent Michaelis constant for the nucleotide coenzymes but the maximum velocity was decreased. 6. The binding between the modified enzyme and NADPH was impaired.