Albumin Hawkes Bay; a low level variant caused by loss of a sulphydryl group at position 177.
A slow migrating minor albumin component, representing 5% of total circulating albumin, was detected by routine serum protein electrophoresis and immunofixation. After treatment with 5 mM dithiothreitol the abnormal component was found to migrate normally suggesting the attachment of some component to the free thiol at position 34. However, purification and analysis by SDS-PAGE showed that the abnormal component had a slightly lower apparent molecular weight than normal albumin. Limited tryptic cleavage indicated the abnormal site to be in the N-terminal third of the molecule. HPLC analysis of tryptic peptides from this domain showed the presence of a new peptide of sequence Ala-Ala-Phe-Leu- Leu-Pro-Lys, indicating either a point mutation of 177 Cys-->Phe or the deletion of residues 166-177. DNA sequencing of PCR-amplified DNA confirmed the former Cys-->Phe substitution by indicating a point mutation of C to A at nucleotide position 5185. It appears that the aberrant electrophoretic mobility of the variant might be due to a gross conformational change associated with the formation of a new disulphide bond between Cys-168 and Cys-124.
Brennan
S O
SO
Molecular Pathology Laboratory, Clinical Biochemistry Unit, Christchurch, New Zealand.
Fellowes
A P
AP
D000368:Aged; D000595:Amino Acid Sequence; D001483:Base Sequence; D004229:Dithiothreitol; D005260:Female; D006801:Humans; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry / Q000302:isolation & purification*; D010949:Plasma / Q000737:chemistry; D011487:Protein Conformation; D012709:Serum Albumin / Q000737:chemistry* / Q000235:genetics; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D013439:Sulfhydryl Reagents; D014357:Trypsin
D010446:Peptide Fragments; D012709:Serum Albumin; D013438:Sulfhydryl Compounds; D013439:Sulfhydryl Reagents; D014357:Trypsin; D004229:Dithiothreitol