title: Structural relationship between alpha 1-microglobulin from man, guinea-pig, rat and rabbit.
abstract: Rabbit alpha 1-microglobulin was purified from the urine of sodium-chromate-treated animals by the use of gel chromatography on Sephadex G-100, affinity chromatography on concanavalin-A--Sepharose and ion-exchange chromatography on DEAE-Sephadex. Rabbit alpha 1-microglobulin had a molecular mass of 25.6 kDa on SDS/polyacrylamide gel electrophoresis. Alpha 1-microglobulin has previously been purified from the urine of humans, guinea-pigs and rats by similar methods, and the molecular masses of the four homologues were compared by SDS/polyacrylamide gel electrophoresis and gel chromatography in a denaturing medium. By these two methods the human homologue was 6 kDa and 3 kDa larger, respectively, than the other three proteins. Endoglycosidase F digestion of alpha 1-microglobulin, followed by SDS/polyacrylamide gel electrophoresis, revealed three protein bands in the human alpha 1-microglobulin sample, and only two bands in guinea-pig, rat and rabbit alpha 1-microglobulin, with a gap between each band of 2.6--2.9 kDa. The amino-terminal amino acid sequences of the four homologues were determined and between 72% and 81% homology was seen. The five amino-terminal amino acids present in the other species were missing in guinea-pig alpha 1-microglobulin. Our results indicate that human alpha 1-microglobulin is substituted with two N-linked oligosaccharides, while only one is attached to each of the other alpha 1-microglobulins, and that the extra glycosylamine-linked oligosaccharide in the human protein is attached to asparagine in position 17. Finally it is shown that all four homologues inhibit antigen stimulation of human lymphocytes, a finding which is consistent with our previous suggestion that the N-linked oligosaccharides carry the immunosuppressive activity of alpha 1-microglobulin.
mesh_terms: D000510:Alpha-Globulins / Q000302:isolation & purification / Q000494:pharmacology / Q000502:physiology / Q000652:urine*; D000595:Amino Acid Sequence; D000818:Animals; D002478:Cells, Cultured; D004261:DNA Replication / Q000187:drug effects; D006026:Glycoside Hydrolases; D006168:Guinea Pigs; D006801:Humans; D008214:Lymphocytes / Q000166:cytology / Q000187:drug effects / Q000276:immunology; D017038:Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase; D008969:Molecular Sequence Data; D008970:Molecular Weight; D011817:Rabbits; D051381:Rats; D012016:Reference Values; D013045:Species Specificity
chemical_list: D000510:Alpha-Globulins; C016001:alpha-1-microglobulin; D006026:Glycoside Hydrolases; D017038:Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase