Differential effects of pyridoxal 5'-phosphate on lysine residues in rabbit and sturgeon muscle aldolases.

Pyridoxal 5'-phosphate (PLP) in aqueous solutions can form a Schiff base complex with 14 and 16 lysine residues of rabbit and sturgeon muscle aldolases (EC 4.1.2.13), respectively. Although the mechanism of their interaction with PLP should be the same, these residues can be differentiated into three families on the basis of their inhibition constant Ki and rate constant k. The lysine residues of one of these families do not react with PLP in the presence of the substrates. Therefore, they are assumed to be part of the active center. In the sturgeon muscle aldolase, 3.7 substrate protected lysine residues are present. Rabbit aldolase, although tetrameric, contains only 2.8 substrate protected lysine residues. This suggests that one active center of this enzyme may be 'buried'. Structural studies showed the following sequence around the substrate protected lysine residues, in the rabbit aldolase: Gly-(Gly2, Val3)-Pyridoxyl Lys-Ile-Asp-Lys.