Interaction of Zn 2+, and Cu 2+, Ions with glyceraldehyde-3-phosphate dehydrogenase from bovine heart and rabbit muscle

Abstract

1. 1. Binding of Zn 2+, and Cu 2+, ions to GAPDHs from bovine heart and rabbit muscle resulted in a partial loss of enzymatic activity of both enzymes, in a time and metal ion concentration dependent manner. Cu 2+, ions caused a much larger decrease of the activity than Zn 2+, ions. 2. 2. Addition of NAD 2+, or EDTA to either enzyme resulted in a protective effect on GAPDH activity. A similar protective effect was observed following addition of 2-mercaptoethanol to the enzyme solution. 3. 3. The association constant for GAPDH-Zn 2+, complex, calculated from equilibrium dialysis data, was 0.9 × 10 4M −1 for the bovine heart GAPDH and 1.3 × 10 4M −1, for the rabbit muscle enzyme. The association constant for GAPDH-Cu 2+, complex was the same for both enzymes, 11.3 × 10 4M −1. 4. 4. Equilibrium dialysis data also revealed that in either enzyme the specific sites, binding the metal ions, are identical or very similar, and independent from each other. They are situated in the most conserved part of the enzyme molecule. 5. 5. Some zinc was found in GAPDH preparations from bovine heart. It is discussed if Zn 2+, ions could have a kind of modulation effect on GAPDH activity.