title: Isolation and characterization of human glucose-6-phosphate isomerase isoforms containing two different size subunits.
abstract: Previously undetected isoforms of human glucose-6-phosphate isomerase (GPI) have been isolated utilizing substrate-induced elution of the enzyme from spherical cross-linked phosphocellulose as an affinity ligand and subjected to a series of physical and chemical studies. The two major isoforms (1, 48%, pI 9.13; 2, 36%, pI 9.00) are homodimers of subunits of 63.2 kDa (Type-A) and are charge isomers, probably representing deamidation of specific Asn-Gly sequences as in other species. Isoform 3 (13%, pI 8.84) is a heterodimer composed of the Type-A subunit and a previously unreported larger subunit of 69.8 kDa (Type-B). Isoform 4 (3%, pI 8.62) is a BB-homodimer. Structural differences in the two types of subunits are also apparent from CNBr fragmentation patterns. Carbohydrate analyses show that, even though potential N- and O-linked glycosylation sites exist, the isoforms are not due to glycosylation. Recently recognized sequence similarities between GPI and the neurotropic lymphokine, neuroleukin (NLK) suggest that GPI and NLK are either derived from the same gene or represent modifications of the same protein. The possibility of NLK-GPI dimers exists, but the new isoforms identified in this study do not appear to represent hybrids of GPI subunits with mature NLK.
authors.affiliation: Department of Biochemistry, University of North Texas/Texas College of Osteopathic Medicine, Fort Worth 76107.
authors.forename: A Q
authors.initials: AQ
authors.lastname: Sun
authors.forename: K U
authors.initials: KU
authors.lastname: Yüksel
authors.forename: T M
authors.initials: TM
authors.lastname: Jacobson
authors.forename: R W
authors.initials: RW
authors.lastname: Gracy
mesh_terms: D000596:Amino Acids / Q000032:analysis; D002241:Carbohydrates / Q000032:analysis; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D005956:Glucose-6-Phosphate Isomerase / Q000302:isolation & purification* / Q000378:metabolism; D006801:Humans; D007525:Isoelectric Focusing; D007527:Isoenzymes / Q000302:isolation & purification* / Q000378:metabolism; D007700:Kinetics; D046911:Macromolecular Substances; D008970:Molecular Weight; D010920:Placenta / Q000201:enzymology*; D011247:Pregnancy
chemical_list: D000596:Amino Acids; D002241:Carbohydrates; D007527:Isoenzymes; D046911:Macromolecular Substances; D005956:Glucose-6-Phosphate Isomerase