Inter-α-Trypsin Inhibitor and Its Related Proteins in Syrian Hamster Urine and Plasma1.

Urinary excretion of trypsin inhibitor increased after injection of a carcinogen, N-nitro sobis(2-oxopropyl)amine, into Syrian hamsters. Two inhibitors were purified to apparent homogeneity from urine collected during the course of the carcinogenesis experiment. Their complete amino acid sequences were determined by Edman degradation of the intact proteins and partially degraded fragments. One corresponded to a hamster liver cDNA clone that hybridized with human bikunin probe [Ide et al. (1994) Biochim. Biophys. Acta 1209,286-292], except that the protein sequence lacked C-terminal serine and the other was trypstatin, the C-terminal half of the bikunin molecule. Three proteins containing covalently linked bikunin were also identified in pooled blood plasma. They were all dissociated into heavy and light chains by treatment with chondroitinase ABC or 50 mM NaOH, but not by heating at 100°C in the presence of sodium dodecyl sulfate and dithiothreitol. N-terminal amino acid sequence analyses of the native chains and partially degraded fragments thereof revealed that these proteins are (i) human-type inter-α-trypsin inhibitor, consisting of heavy chains 1 and 2 and bikunin, (ii) bovine-type inter-α-trypsin inhibitor, consisting of heavy chains 2 and 3 and bikunin, and (iii) pre-α-trypsin inhibitor, consisting of heavy chain 3 and bikunin. Heterodimer of bikunin/heavy chain 1 or bikunin/heavy chain 2 was not detected. These results suggest that the composition, and hence function, of the Inter α-trypsin inhibitor family differs considerably from species to species. [ABSTRACT FROM AUTHOR]