title: Sequestration and degradation of alpha 2u-globulin in rat kidney lysosomes.
abstract: alpha 2u-Globulin (M.W. = 18,709) is the major protein synthesized in the liver of adult male rats. alpha 2u-Globulin, secreted from the liver, is filtered by the kidneys where about a half of the protein is reabsorbed and the remainder is excreted in the urine. Highly purified lysosomes from rat kidneys were subjected to immunoblot analysis using antiserum against alpha 2u-globulin. A major immuno-reactive band was observed at the position about 1 k dalton smaller than that of the authentic alpha 2u-globulin. The immuno-reactive band in SDS-polyacrylamide gel was excised and the protein, eluted from the gel, was subjected to amino acid sequence analysis by micro Edman method. The N-terminal amino acid sequence of the intralysosomal alpha 2u-globulin was found to be leu-asp-val-ala-lys-leu-asn-gly-... which exactly corresponded to the sequence from the 10th leucine residue of the authentic urinary alpha 2u-globulin. This result suggests that alpha 2u-globulin, sequestered into the kidney lysosomes, is cleaved intralysosomally between the 9th asparagine and the 10th leucine, and the degradative intermediate, thus produced, is accumulated in the lysosomes. The immuno-blot assay gave the value of 210 +/- 70 mg alpha 2u-globulin/g kidney lysosomal proteins. The molecular basis for the resistance of the degradative intermediate of alpha 2u-globulin against further degradation in the kidney lysosomes was discussed in the light of the computer-predicted secondary structure of alpha 2u-globulin.
authors.forename: K M
authors.initials: KM
authors.lastname: Khan
mesh_terms: D000510:Alpha-Globulins / Q000032:analysis / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D005260:Female; D015151:Immunoblotting; D007668:Kidney / Q000648:ultrastructure*; D008099:Liver / Q000648:ultrastructure; D008247:Lysosomes / Q000032:analysis / Q000378:metabolism*; D008297:Male; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000378:metabolism; D011487:Protein Conformation; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D000510:Alpha-Globulins; D010446:Peptide Fragments; C013803:alpha 2u globulin