Isolation and characterization of two distinct mannan-binding proteins from rat serum.
Two binding proteins, which are specific for mannose and N-acetylglucosamine, were isolated from rat serum to homogeneity. The minor component [serum mannan-binding protein I (S-MBP-I)] was indistinguishable from rat liver mannan-binding protein (L-MBP). S-MBP-I had a molecular mass of about 200 kDa and consisted of about six identical 32-kDa subunits; the molecule had a collagen-like structure, and its properties were identical to those of L-MBP. S-MBP-I was also indistinguishable from L-MBP in immunochemical reactivity. Furthermore, the sequence of 15 NH2-terminal amino acids of S-MBP-I was identical to that of L-MBP, the complete primary structure of which has been elucidated [Drickamer, K., Dordal, M. S., and Reynolds, L. (1986) J. Biol. Chem. 261, 6878-6887; Oka, S., Itoh, N., Kawasaki, T., and Yamashina, I. (1987) J. Biochem. 101, 135-144]. The major component (S-MBP-II) had a molecular mass of about 650 kDa and consisted of about 20 identical 31-kDa subunits; it was immunochemically distinct from L-MBP and S-MBP-I, although the molecule had a collagen-like structure similar to L-MBP and S-MBP-I. Metabolic studies using [3H]leucine showed that S-MBP-II is a typical plasma protein turning over with a half-life of 1.6 days. S-MBP-I was unusual in its late appearance and rapid turnover rate in plasma. These results, together with the fact that L-MBP decayed with biphasic curves, suggest that a part of L-MBP is leaked from liver into plasma in the form of S-MBP-I.
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002352:Carrier Proteins / Q000097:blood / Q000302:isolation & purification* / Q000378:metabolism; D037222:Collectins; D005779:Immunodiffusion; D007700:Kinetics; D037102:Lectins / Q000097:blood / Q000302:isolation & purification* / Q000378:metabolism; D008099:Liver / Q000032:analysis; D008297:Male; D008351:Mannans / Q000097:blood; D008657:Metabolic Clearance Rate; D008969:Molecular Sequence Data; D008970:Molecular Weight; D011485:Protein Binding / Q000187:drug effects; D051381:Rats; D011919:Rats, Inbred Strains
D000596:Amino Acids; D002352:Carrier Proteins; D037222:Collectins; D037102:Lectins; D008351:Mannans; D002118:Calcium