GAPDH was speculated to function as a transient trap to reduce the potential toxicity of free heme by a specific and reversible binding with heme. Up to now, there has been lack of studies focused on this effect. In this paper, the efficiency of GAPDH-heme complex on catalyzing protein carbonylation and nitration, the cross-linking of heme to protein formation, and cytotoxicity of GAPDH-heme were studied. It was found that the binding of GAPDH could inhibit H2O2-mediated degradation of heme. Peroxidase activity of GAPDH-heme complex was higher than that of free heme, but significantly lower than that of HSA-heme. Catalytic activity of heme corresponded complex toward tyrosine oxidation/nitration was decreased in the order of HSA-heme, heme and GAPDH-heme. GAPDH also inhibited heme-H2O2-NO2- induced protein carbonylation. No covalent bond was formed between heme and GAPDH after treated with H2O2. GAPDH was more effective than HSA on protecting cells against heme-NO2--H2O2 induced cytotoxicity. These results indicate that binding of GAPDH inhibits the activity of heme in catalyzing tyrosine nitration and protects the coexistent protein against oxidative damage, and the mechanism is different from that of HSA. This study may help clarifying the protective role of GAPDH acting as a chaperone in heme transfer to downstream areas.
Keywords: Glyceraldehyde-3-phosphate dehydrogenase; Heme; Peroxidase activity; Protein carbonylation; Tyrosine nitration.
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