RELATIONSHIP BETWEEN THE STABILITY AND AUTOXIDATION OF MYOGLOBIN

The rate of autoxidation and the free energy of guanidine hydrochloride denaturation of myoglobin from sperm whale, horse, mackerel, skipjack, and bluefin, yellowfin, and bigeye tunas were studied in the pH range from 4.5 to 10.0. Myoglobin from tunas showed minimal autoxidation rate at pH 7.0-8.0 and the highest free energy at pH 7.5-8.0. Higher rates of autoxidation and lower values of free energy were observed at lower or higher pH values. The myoglobin stability was in the order bluefin tuna > yellowfin tuna > bigeye tuna, and the autoxidation rates showed the contrary order: bigeye tuna > yellowfin tina > bluefin tuna. The pH dependency of myoglobin from skipjack, mackerel, horse, and sperm whale was similar. Lower myoglobin stability was associated with higher autoxidation rate. High correlation coefficients between the rate constant and the free energy were observed.