The rate of autolysis after thawing in intact frozen krill (whole body, cephalothorax, and abdomen) and in its homogenates was studied by determining both the increase of TCA-soluble nitrogen and the change of protein pattern in SDS-polyacrylamide gel electrophoresis. Autolysis in the intact state proceeded rapidly in the separated cephalothorax, but very slowly in separated abdomen. The pH dependence in autolysis differed between cephalothorax and abdomen homogenates, indicating differences in the proteolytic enzymes involved. Autolysis of intact whole body proceeded to an extent similar to that of intact cephalothorax, liberating about 30% of total nitrogen in 24 hr. The rapid autolysis of abdomen proteins in the intact whole body was attributed to the action of cephalothorax proteases which penetrate into abdomen. Amongmuscle proteins, the myosin heavy chain (MW=206,000) was degraded very rapidly

Cathepsin A [EC 3.4.2.-] of small molecular size (cathepsin A, S) has been purified about 800-fold from pig kidney by procedures including chromatographies on DEAE-Sephadex, SP-Sephadex, and Sephadex G-150. 1. The homogeneity of the purified enzyme was proved by ultracentrifugation and polyacrylamide gel electrophoresis. The molecular weight (100,000) and isoelectric point (pI=5.0) were estimated. 2. The enzyme was remarkably stabilized by sucrose and KCl, and was most stable at pH 5-5.5 in the presence of both stabilizers. The enzyme had not only peptidase activity but also esterase and amidase activity; it was optimally active at pH 5.2 for peptide hydrolysis and at pH 8 for the hydrolysis of esters and amides. 3. Diisopropyl fluorophosphate and iodoacetamide completely inhibited these three activities. 4. The enzyme hydrolyzed various benzoyl- and benzyloxycarbonyl-dipeptides with neutral, acidic, and basic amino acids, and proline in the C-terminal position. The carboxypeptidase nature of the enzyme was proved by its action on an oligopeptide. 5. Several enzymatic properties of cathepsin A, S were almost the same as thoas of cathepsin A of large molecular size (cathepsin A, L) and the crude homogenate.

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The presence in wheat flour of several kinds of proteases was shown on the basis of pHactivity profile, substrate specificity, and response to inhibitors. Amongthem, 14C-hemoglobin and cbz-Phe-Ala hydrolases (14C-Hbase and CPAase) showed optimal activity around pH 4. 14C-Hbase was inhibited almost completely by pepstatin, and CPAase was partially inhibited by DFP. About 85% of 14C-Hbase activity and 40% ofCPAase activity in the original flour were retained in gluten fraction. The decrease in viscosity of the gluten solution in dilute acetic acid was effectively prevented by pepstatin. An SDS-PAGEpattern showed that hydrolysis of gluten proteins was prevented effectively by pepstatin, although not completely, and that the simultaneous addition of pepstatin and DFP prevented completely self-digestion of the gluten proteins. Therefore, pepstatin and DFPsensitive proteases were shownto be responsible for the self-digestion of gluten proteins. The modeof action of these enzymeswasrelatively specific for the secondhighest molecular weight subunit of glutenin and for some other proteins.

In order to determine which proteases are responsible for the autolysis of krill, the effects of several protease inhibitors on the autolysis and protease activities of krill were investigated. Homogenatesof whole bodies, and the cephalothorax and abdomen parts of frozen krill were equilibrated at 37°C at different pHs between 2 to 10 and allowed to stand for 16hr, following which the increase in the TCA soluble fraction was monitored. 14C-Hemoglobin (14C-Hb)

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