Identification of a Tissue Inhibitor of Metalloproteinase-2: An Endogenous Inhibitor of Modori-Inducing Insoluble Metalloproteinase from Yellowtail Seriola quinqueradiata Muscle

The existence of an endogenous protease inhibitor (EPI) was expected from the comparison of the gel properties between washed and nonwashed yellowtail surimi gels. A possible candidate, tissue inhibitor of metalloproteinase-2 (TIMP-2), was partially purified from the soluble fraction of yellowtail muscle, and an 18 kDa protein band was detected by sodium dodecyl-sulfate polyacrylamide gel electrophoresis (SDS-PAGE) under nonreducing conditions and western blot analysis. Its N-terminal amino acid sequence was determined as XSXSPAHPQQAF, with high homology to TIMP-2 from other fish species, suggesting that it was identified as yellowtail TIMP-2. Subsequently, full-length cDNA of two isoforms (TIMP-2a and TIMP-2b) was successfully cloned from yellowtail muscle. The N-terminal sequence of purified TIMP-2 completely corresponded to TIMP-2b. When the surimi gel quality decreased after spawning, the mRNA expression of TIMP-2b also decreased. Human TIMP-2 could inhibit autolysis of myofibrillar proteins from yellowtail muscle. Thus, TIMP-2b was considered the major EPI of the modori-inducing insoluble metalloproteinase in yellowtail muscle.