Identification by Fast Atom Bombardment Mass Spectrometry of HB Indianapolis [β112(G14)CYS→ARG] in a Family from Naples, Italy

Abstract

We have characterized a β112 Arg hemoglobin in an individual from Naples, Italy, with minimal clinical problems- Blood tests revelead only slight reticulocytosis and hemoglobin instability. Furthermore, high value of alkali resistance tests for Hb F were observed. Isoelectricfocusing of globins showed the occurrence of a band migrating between the normal α and β globin chains. The fairly stable variant chain was purified by fast protein liquid chromatography. A mass map of the tryptic digest was obtained by fast atom bombardment mass spectrometry clearly showing that we were dealing with a β chain variant. However, the peptide 105-120 was missing and two new ones were present, i.e.: 105-112 and 113-120; we assumed these peptides to be generated because of the substitution of 112 Cys with an arginine residue. Further confirmation stemmed from the fast atom bombardment mass spectra of the tryptic digest submitted to a single Edman degradation step and to carboxypeptidase B further hydrolysis. The β-globin chain variant was thus mass mapped to an extent of about 98%. Such a variant, named Hb Indianapolis, was first reported by Adams et al (1, 2) as an extremely unstable variant producing the phenotype of a severe β-thalassemia. Contrary to the findings of the above authors the occurrence of the same variant in a clinically normal individual from a Spanish family has recently been reported (3). Because the clinical manifestations in the latter case are similar to those observed by us, the conclusion can be drawn that β 112 Arg hemoglobin is not a biologically unstable variant but should be regarded as belonging to the class of unstable hemoglobins giving rise to only marginal clinical problems.