title: Distribution of manganese in rat pancreas and identification of its primary binding protein as pro-carboxypeptidase B.
abstract: Distribution of manganese (Mn) and its binding to specific proteins were examined in rat pancreas. A MnCl2 solution was injected subcutaneously into Wistar rats daily at a single dose of 15 mg of Mn/kg body weight for 10 days and the animals were killed 1 day after the last injection. The concentration of Mn in the pancreas increased considerably from 1.4 +/- 0.2 (control) to 13.3 +/- 3.7 micrograms/g wet tissue by the repeated injection of Mn. The distribution of Mn in the soluble fraction of the pancreas (170,000 g supernatant) was determined on a gel-filtration column (Asahipak GST-520) using an h.p.l.c.-inductively coupled argon plasma atomic-emission spectrometry (i.c.p.) technique. The metal was eluted as a single peak in the high-molecular-mass protein fraction, where Mn had been observed as a small peak in the control profile, suggesting that the administered Mn was bound to the same Mn-binding component as that in the control. On the basis of enzymic and chemical characterization of the protein, it was identified as a zymogen of carboxypeptidase B (pro-carboxypeptidase B, pro-CPB). The elution profiles of the protein by h.p.l.c.-i.c.p. indicated that Mn and zinc (Zn) were bound to the zymogen with a molar ratio of 1:4 in normal rat pancreas. Mn bound to the zymogen was easily replaced by Zn in vitro, suggesting that Mn was bound to the Zn-binding site and that the binding affinity to Zn was higher than that to Mn. The present results indicate that pro-CPB is the primary Mn-binding protein in the pancreas of control and also Mn-administered rats.
authors.affiliation: National Institute for Environmental Studies, Ibaraki, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Kodama
authors.forename: N
authors.initials: N
authors.lastname: Shimojo
authors.forename: K T
authors.initials: KT
authors.lastname: Suzuki
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D043424:Carboxypeptidase B; D002268:Carboxypeptidases / Q000737:chemistry / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D004792:Enzyme Precursors / Q000737:chemistry / Q000378:metabolism*; D008297:Male; D008345:Manganese / Q000032:analysis* / Q000378:metabolism / Q000494:pharmacology; D008969:Molecular Sequence Data; D010179:Pancreas / Q000737:chemistry* / Q000187:drug effects / Q000378:metabolism; D011485:Protein Binding; D051381:Rats; D011919:Rats, Inbred Strains; D014018:Tissue Distribution
chemical_list: D004792:Enzyme Precursors; D008345:Manganese; D002268:Carboxypeptidases; D043424:Carboxypeptidase B