Cathepsins B and L and cathepsin L-like proteinase degraded myosin heavy chain of actomyosin (AM) into several fragments with molecular masses (MW) of 154, 146, 138, 67, and 36 kDa; 164 and 155 kDa; and 135, 128, and 69 kDa, respectively. In the presence of 0.6 M NaCl, however, the MHC was degraded by cathepsin L into 164, 155, 41, and 37 kDa fragments. The hydrolytic rate of these three proteinases on AM was faster at pH 5.0 than at pH 6.0. Actin seemed to be resistant against hydrolysis by cathepsins B, L, and L-like in the absence of 0.6 M NaCl. According to SDS−PAGE analysis, cathepsin X, a novel cysteine proteinase, did not degrade AM. Keywords: Mackerel; cathepsins; actomyosin; proteolysis; seafood

A method for the detection of N-acetylglucosaminidase (GlcNAcase) activity has been developed by using 4-methyl-umbelliferyl-N-acetyl-D-glucosaminide (4-MU-GlcNAc) as substrate in crossed immunoelectrophoresis (CIE) and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) gels. Visualization of the reaction with a 366 nm ultra-violet light is possible in approximately 30 min. The method is fast and sensitive in comparison with previous methods. The same band as in SDS-PAGE, showing both GlcNAcase and chitinase activity, was found in the present study; we therefore conclude that this method is also useful in a GlcNAcase-type chitinase assay.

The NADPH-sulfite reductase from Saccharomyces cerevisiae was purified to electrophoretic homogeneity by ammonium sulfate fractionation, DEAE Sephacel, Sephacryl S-300 and DEAE Sephadex A-50 chromatography. Optimal pH was 7.3 and temperature 25°C. It was inhibited by IAA, PCMPS, PMSF, NEM, PCMB, cyanide and most divalent metal ions. For the ozonated mackerel surimi ground with purified reductase, the reactive SH increased from 2.29∞10 5 to 4.46∞10 5 mole/g and gel strength from 256.7 to 360.5g·cm. According to SDS-PAGE, the recovery of myosin heavy chain was observed on the ozonated mackerel surimi with addition of NADPH-sulfite reductase.