Identification of a protein increasing in serum of Nagase analbuminemic rats bearing intestinal tumors as an isotype of T-kininogen

Increase in an unidentified protein was observed in serum of Nagase analbuminemic rats (NAR) bearing intestinal tumors induced by azoxymethane. This protein seemed to be a polymer of a protein of 73 kDa as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and so was tentatively named 73K-protein. The serum concentration of 73K-protein in NAR bearing intestinal tumors was 11.9 +/- 2.2 mg/ml (mean +/- SD, n = 5), whereas that in control NAR was 2.0 +/- 0.2 mg/ml. Increase of the serum 73K-protein level was also observed in Sprague-Dawley rats bearing intestinal tumors, skin tumors, subcutaneous sarcomas, or mammary tumors and in ACI rats bearing urinary bladder tumors. On double immunodiffusion analysis, the 73K-protein was not detected in mouse, guinea pig, pig, horse, or human serum. A cDNA clone bearing the sequence encoding 73K-protein was isolated from a cDNA library constructed from rat liver mRNA. The nucleotide sequence of the 73K-protein showed 98.8% and 96.9% homologies with the sequences of the 3'-proximal domains of the cDNAs for TI- and TII-kininogen, respectively. Therefore, the 73K-protein was concluded to be an isotype of T-kininogen.