What Is Cyanmethemoglobin?

Abstract

Since previous workers 1 have explained the action of nitrites and methylene blue in cyanide poisoning as the formation of methemoglobin by these substances and the consequent union of CN with the methemoglobin to form cyanmethemoglobin, I was interested in finding out what constituted cyanmethemoglobin.

The literature is rather vague concerning this substance. The few brief descriptions are not quantitative and there seems to be a dispute as to its chemical configuration. 2

I therefore studied the effects of either or both KCN and NaNO₂ on the spectrophotometric picture of oxyhemoglobin and reduced hemoglobin. The amount of NaNO₂ employed was sufficient to change 88% of the oxyhemoglobin to methemoglobin, and the chemically equivalent amount of KCN was used. The resulting hemoglobin derivatives were examined spectrophotometrically.

Oxyhemoglobin was formed by vigorous shaking either in air or oxygen; reduced hemoglobin by means of Stokes Reagent according to the usual procedure; methemoglobin, by adding NaNO₂. In vitro experiments with sheep, rat and rabbit blood and in vivo experiments with rabbit and rat gave essentially similar results. The experiments here reported were done with sheep red blood cells in vitro. To each 2 cc. of defibrinated blood which had been washed several times and made up to original volume in 0.9% NaCl was added 0.2 cc. of 0.33 M NaNO₂ and/or KCN according to the experiment. For spectrophotometric examination 1 cc. of the resulting suspension was hemolyzed in 100 cc. of 0.4% NH₄OH.

In no case did the absorption spectrum in the presence of KCN differ qualitatively from that of oxyhemoglobin. The ratio of the extinction coefficients at 540 and 560 mμ was calculated and is given as R in Table I. This ratio indicates according to Ray, Blair and Thomas 3 the proportion of oxyhemoglobin in mixtures with reduced or methemoglobin.