Four intracisternal calcium-binding glycoproteins from rat liver microsomes with high affinity for calcium. No indication for calsequestrin-like proteins in inositol 1,4,5-trisphosphate-sensitive calcium sequestering rat liver vesicles.
It has been claimed that the inositol 1,4,5-trisphosphate-sensitive calcium pool in liver and pancreatic acinar cells is located in specified organelles ("calciosomes") which are characterized by their content of the calcium-binding protein calsequestrin (Volpe, P., Krause, K. H., Hashimoto, S., Zorzato, F., Pozzan, T., Meldolesi, J., and Lew, D. P. (1988) Proc. Natl. Acad. Sci. U. S. A. 85, 1091-1095). We show here that the inositol 1,4,5-trisphosphate-sensitive compartment of rat liver does not contain calsequestrin-like material. Instead four non-membraneous calcium-binding glycoproteins with approximate molecular masses of 59, 60, 80, and 90 kDa were found. The 59-, 80-, and 90-kDa proteins were of the high mannose-rich type, the carbohydrate moiety of the 60-kDa protein was of the complex hybrid type with terminal galactoses. All four proteins had high affinity binding sites for calcium (KD between 1 and 5 microM) and from 1 to 5 binding sites/molecule. The 80- and the 90-kDa proteins had also low affinity binding sites (KD 400 and 600 microM, respectively, with 13 and 15 binding sites/molecule, respectively). A comparison of the NH2-terminal sequences revealed that the 60-kDa calcium-binding protein represents the rat liver calregulin, whereas the 90-kDa calcium-binding protein represents grp94. The sequences did not reveal any relationship of the 80-kDa protein with grp78, or of the 59-kDa protein with protein disulfide isomerase.
Van
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Zentrum Innere Medizin, Universität Göttingen, Federal Republic of Germany.
Peter
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Söling
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D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000032:analysis* / Q000378:metabolism; D037282:Calreticulin; D002155:Calsequestrin / Q000032:analysis; D004721:Endoplasmic Reticulum; D005690:Galactose / Q000032:analysis; D006023:Glycoproteins / Q000032:analysis* / Q000378:metabolism; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology*; D008297:Male; D008358:Mannose / Q000032:analysis; D008862:Microsomes, Liver / Q000737:chemistry* / Q000187:drug effects; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009132:Muscles / Q000737:chemistry; D010766:Phosphorylation; D051381:Rats; D011919:Rats, Inbred Strains; D012261:Ribonucleoproteins / Q000032:analysis* / Q000378:metabolism
D002135:Calcium-Binding Proteins; D037282:Calreticulin; D002155:Calsequestrin; D006023:Glycoproteins; D012261:Ribonucleoproteins; D015544:Inositol 1,4,5-Trisphosphate; D008358:Mannose; D002118:Calcium; D005690:Galactose