INTRACORPUSCULAR METHÆMOGLOBIN FORMATION AND ITS RELATION TO THE RATE OF OXYGEN RELEASE

1. The relative rate of O 2 release from horse r.b.c. suspensions (pH 7·0–7·4) measured with a slow reaction method was investigated in relation to the methæmoglobin formation. 2. A straight‐line relationship was found between the relative rate of methæmoglobin formation by sodium nitrite and the increase in the rate of O 2 release. 3. A close relationship was also found between the increase in the rate of O 2 release and the relative rate of the spontaneous methæmoglobin formation caused by exposure of the r.b.c. suspensions to N 2 + CO 2 gas mixtures. 4. A methæmoglobin formation uninterrupted by the reduction develops in the suspensions poisoned by sodium azide. The phenomenon is probably caused by a combination between sodium azide and spontaneously formed methæmoglobin [Keilin], this compound being resistant to the intracorpuscular enzymatic reduction of the preformed methæmoglobin. Sodium azide also causes an increase in the rate of O 2 release from r.b.c. suspensions. 5. A suggestion is forwarded of a possible part played by the spontaneous methæmoglobin formation as a factor promoting deoxygenation.