PMID: 6165715Jun 10, 1981Paper

The carbamate equilibrium of alpha- and epsilon-amino groups of human hemoglobin at 37 degrees C.

The Journal of Biological Chemistry
G GrosR E Forster

Abstract

We have investigated the carbamate equilibrium of human adult hemoglobin, human cord blood hemoglobin, methemoglobin, and carbamylated hemoglobin using a stopped flow, rapid reaction pH apparatus described previously. The carbamate formation of human adult hemoglobin at 37 degrees C and ionic strength 0.15 was measured at pH values ranging from 6.2 to 8.8 and at CO2 partial pressures between 15 and 140 Torr. From experiments with unmodified hemoglobin as well as with hemoglobin specifically carbamylated at the four NH2 termini, it was found that already at pH 8, the epsilon-amino groups contribute significantly to carbamate formation in addition to the alpha-amino groups. At pH 8.5, about 70% of the total carbamate is due to epsilon-amino groups. The carbamate formation of alpha- and epsilon-amino groups can be suppressed by complete carbamylation of the hemoglobin. The results obtained from human adult deoxy- and oxyhemoglobin were used to calculate the equilibrium constants governing carbamate formation of these hemoglobins: Kc, the carbamate equilibrium constant, Kz, the R-NH2 ionization constant, and n, the number of binding sites per hemoglobin tetramer. Accordingly, two types of alpha-amino groups, each comprising two gro...Continue Reading

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