Hemoglobin Gorwihl [α2β25(A2)Pro→Ala], an Electrophoretically Silent Variant with Impaired Glycation

Abstract

BACKGROUND: Some of the genetic variants of hemoglobin (Hb) and their chemically modified species are known to affect the measurement of Hb A(1c). The purpose of this study was to characterize Hb species in the blood sample of a 74-year-old German male with an exceptionally low Hb A(1c) value. METHODS: Hemolysates from the propositus and a healthy individual were analyzed by electrophoresis, cation-exchange HPLC, boronate affinity chromatography, and electrospray ionization-mass spectrometry (ESMS). Genomic DNA was amplified by PCR, and the sequencing was performed on an ABI 310 sequencer. Functional properties of Hb were determined by oxygen equilibrium studies and CO recombination kinetics after flash photodissociation. Glycohemoglobin species were synthesized by incubating hemolysates with glucose. RESULTS: A novel, electrophoretically silent beta chain, beta5(A2)Pro-->Ala or Hb Görwihl, was detected by cation-exchange HPLC. It accounted for approximately 44% of the total Hb and had functional properties similar to those of normal Hb A and a mild degree of heat instability. During incubation with glucose, glycation of the beta chains (assessed by ESMS) in the hemolysate of a healthy volunteer was twice as fast as in hemolysate from the propositus. CONCLUSIONS: The substitution beta5(A2)Pro-->Ala seems to affect neither the functional properties nor the heterotropic interactions of Hb, but slows glycation of the N-terminal valine by an unknown mechanism.