Postsynthetic deamidation of hemoglobin providence (β 82 Lys → Asn, Asp) and its effect on oxygen transport

Carriers of hemoglobin Providence have three types of β chain in their hemolysates. The two abnormal chains have asparagine (Providence N, Prov N) or aspartic acid (Providence D) at position β 82, instead of lysine. In vitro, only two β chains are synthesized by reticulocytes of carriers, β(A) and β(provN). In vivo studies showed that the specific activity of Providence N was initially 10 fold higher than that of Providence D; the specific activities of the two labeled hemoglobins were approximately equal 5 wk after injection of isotope. Oxygen affinity of carriers' blood was somewhat increased, but they were not polycythemic. The affinity of the purified hemoglobins Providence was decreased. Addition of 2, 3 diphosphoglycerate had little effect on the affinity of either hemoglobin component, and addition of inositol hexaphosphate produced no change in the affinity of Providence D. These studies demonstrate that Providence N is deamidated to Providence D during the life span of the erythrocyte, and suggest this finding may represent only an easily observed prototype of posttranslational modification of proteins in general. Despite an abnormal P₅₀ of the blood, oxygen transport is probably normal in carriers of the abnormal hemoglobins.