Modori-inducing Proteinase Active at 50.DEG.C. in Threadfin Bream Muscle.

A novel modori-inducing proteinase optimally active at 50°C was purified to apparent homo-geneity from sarcoplasmic fraction of threadfin bream muscle using a combination of chromato-graphies on DEAE-cellulose, hydroxylapatite, Ultrogel AcA34, and TSK-gel G3000SWXL. This proteinase was distinguished from sarcoplasmic 60°C modori-inducing proteinase (Sp-60-MIP) purified from the same species in following points; (1) this novel proteinase degraded myosin heavy chain optimally at 50°C but did not do it at 60°C and (2) the molecular weight of this proteinase (500, 000) was higher than that of Sp-60-MIP (77, 000). However, this novel proteinase was found to share common properties with Sp-60-MIP in the respect of substrate specificity (trypsin-like) and inhibitor spectra (serine proteinase-like). This line of evidence suggests that trypsin-like serine proteinases play important roles in developing modori-phenomenon but major candidates for the phenomenon occurring at 50 and 60°C are clearly distinct.