The effect of divalent metal ions on the thermostability of C3

Thermostability studies on human complement component C3 showed that saturation of the electronegative sites in the C3 molecule with divalent cations offered some protection against heat denaturation, a finding not previously reported in the literature. To inactive C3 in about 30 minutes, the required temperature was 61 degrees C in the presence of excess Ca2+ ions, 59.5 degrees C in the presence of excess of Mg2+ ions, but only 54 degrees C in the absence of these ionized metal ions.