Hb Long Island: a hemoglobin variant with a methionyl extension at the NH2 terminus and a prolyl substitution for the normal histidyl residue 2 of the beta chain.

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Abstract
Hb Long Island was found in a diabetic man and his nondiabetic mother as the result of a routine clinical measurement of Hb AIc. It is present in amounts approximately equal to Hb A. Its .alpha. chains are normal but its .beta. chains have 2 alterations compared to the normal. A methionyl residue is attached to the usual NH2-terminal valyl residue. This valyl residue is followed by prolyl residue in place of the usual histidyl residue 2. The remaining sequence of the .beta. chain is normal. No Hb or abnormal .beta. chain containing only the prolyl substitution could be detected by several different electrophoretic and HPLC [high performance liquid chromatography] procedures. Hb Long Island is the result of a mutation in which a single nucleotide change causes the substitution of a prolyl residue for the normal histidyl residue at position 2 of the .beta. chain. This abnormal prolyl residue inhibits enzymatic cleavage of the initiator methionyl residue from the abnormal .beta. chain during posttranslational processing. Although the O2 affinities of the whole blood, suspended cells and hemolysate are normal, the affinity of the isolated Hb Long Island is slightly decreased and the effects of organic phosphates are reduced compared to normal. These changes are consistent with the loss of the normal histidyl residue 2 and the extension of the NH2-terminal end of the .beta.-chain molecule.