ATP-induced stimulation of calcium binding to cardiac sarcolemma.

The influence of β-93 sulfhydryl groups on the oxidation of human hemoglobin by sodium nitrite was studied. It is shown that the blocking of these groups by iodoacetamine counteracts the inhibition of the hemoglobin oxidation reaction caused by inositol hexaphosphate. This effect is not present under anaerobic condition. However, in the absence of free oxygen (deoxyhemoglobin), blocking of the β-93 sulfhydryl groups accelerates markedly the rate of oxidation which is otherwise very slow. In the light of these observations, it is concluded that the hemoglobin β-93 free-SH groups play a protective role for the heme iron against oxidation. The rapid oxidation of modified hemoglobin by nitrite under anaerobic condition as well as the abolishment of the effect of IHP under aerobic condition by β-93-SH groups blockage argue against the assumption that R conformation is primarily responsible for the rapid oxidation of oxyhemoglobin by nitrite.