Microheterogeneity of rat submaxillary gland kallikrein k10, a member of the kallikrein family

A tissue-kallikrein-related proteinase present in rat submaxillary glands, which was previously called endopeptidase k, has been further characterized and compared with other members of the kallikrein family. The partial primary structure of this proteinase, now called kallikrein k10, is very similar to that of proteinase B [Kato, H., Nakanishi, E., Enjyoji, K., Hayashi, I., Oh-Ishi, S. & Iwanaga, S. (1987) J. Biochem. (Tokyo) 102, 1389-1404] and T-kininogenase [Xiong, W., Chen. L. M. & Chao, J. (1990) J. Biol. Chem. 265, 2822-2827], but no corresponding gene or mRNA has so far been found. Kallikrein k10 is microheterogeneous due to variable glycosylation of its N-terminal light chain and to variable processing at its kallikrein loop, as shown by endo-beta-N-acetylglucosaminidase F treatment, amino acid sequence analysis and mass spectrometry. The enzymatic properties of the two molecular varieties of kallikrein k10 towards synthetic fluorogenic substrates are not significantly different. Both cleave specifically after Arg residues, but, in contrast to true tissue kallikrein, may accommodate either polar or nonpolar residues at position P2. Kallikrein k10 also differs from tissue kallikrein by its sensitivity to soyabean trypsin inhibitor. Its biological function may therefore differ from that of tissue kallikrein, especially as it does not induce a transient decrease in blood pressure when injected in vivo.