Lipoxygenase (LOX) is thought to play an important role in the formation of desirable or undesirable flavor and aroma in many plant products. In rice seeds, LOX activity is localized in the bran fraction and LOX-3 is the major isozyme component. We used gas chromatography-mass spectrometry to determine whether the degree of staleness in the flavor of stored brown rice was related to the presence of LOX-3. We found that the amount of hexanal, pentanal, and pentanol in normal raw LOX-3 rice markedly increased during storage at 35 degrees C. That in LOX-3-less rice increased slightly but was a third to a fifth that of normal LOX-3 rice. In cooked rice, the amount of these components from glutinous rice exceeded that in nonglutinous rice, and that in normal LOX-3 rice exceeded that in LOX-3-less rice. These results indicate that the stale flavor production in LOX-3-less rice during storage is less than that in normal LOX-3 rice.

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Cathepsin B was purified from rabbit skeletal muscle by ammonium sulfate fractionation and successive chromatographies on Sephadex G-75, phosphocellulose, peptide-conjugated Sepharose, DEAE-Toyopearl and Sephadex G-100. The purified enzyme gave a single protein band on SDS/polyacrylamide gel electrophoresis. The enzyme did not abolish the Ca sensitivity of the ATPase activity of myofibrils. The molecular mass of the enzyme was found to be 27 kDa on gel filtration and SDS/polyacrylamide gel electrophoresis. The optimum pH for the hydrolysis of N"-benzoyl-DL-arginine-P-naphthylamide was 6.5. The enzyme was stable in the range of pH 4.5 -5.5. Tetrathionate reacted with thiol groups of the enzyme reversibly so that it stabilized the enzyme. The enzyme was strongly inhibited by iodoacetate, HgC12, antipain, leupeptin, N"-p-tosyl-L-lysine chloromethane and L-tosylphenylalanylchloromethane, but not by pepstatin or trypsin inhibitor.The purification of muscle cathepsin B has already been reported by Schwartz and Bird [I] and Hirao et al. [2]. Schwartz and Bird [l] partially purified the enzyme from rat skeletal muscle and showed that it could degrade myosin. Hirao et al. [2] purified the enzyme to the electrophoretically homogeneous state from monkey skeletal muscle and found that it could degrade myosin and actin. However, in these studies it was not determined at which step of the respective purification process cathepsin B was separated from cathepsin L, which was shown to be present in a crude extract of cathepsin B and to be similar in several properties with cathepsin B in our previous study [3], or whether or not cathepsin L was really excluded from the purified cathepsin B preparation. Therefore, in the present study we established a new method for obtaining rabbit skeletal muscle cathepsin B completely free from cathepsin L, and investigated its properties. MATERIALS AND METHODS MaterialsThe rabbit muscle (longissimus dorsi) was obtained from the carcasses immediately after slaughter and, after removal of fat and connective tissue, it was minced with a meat chopper. Bovine serum albumin, ovalbumin, chymotrypsinogen and cytochrome c were purchased from Boehringer Mannheim Correspondence zo A. Okitani,