Abstract
Direct examination of hemolysate by electrospray ionization mass spectrometry may lead to the rapid ascertainment of variant hemoglobins (Hb) and to the quantification of glycated Hb. Plasma and cell proteins other than Hb can be prepared by immunoprecipitation prior to MS. The detected variants were sequenced by MS using enzyme cleaved peptides. We detected various variants of Hb, transthyretin, and CuZn-superoxide dismutase. New variants included; 1) Hb Sagami [β139 (H17) Asn→Thr], and 2) Hb Hokusetsu [β52 (D3) Asp→Gly]. These were studied to clarify the cause of unusual profiles of HPLC for HbAlc measurement. Hb Sagami was an electrophoretically silent and isopropanol test-negative variant, detected solely by ESIMS. Other new variants included; 3) a variant transthyretin, amyloidogenic, [38 Asp→Ala], and 4) another variant transthyretin, non-amyloidogenic, [101 Gly→Ser]. Variant transthyretins are usually difficult to detect by electrophoresis. Samples containing variant Hb or high carbamylated Hb gave erroneous results of glycated Hb by routine HPLC and immunoassay, but did not by MS.
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