A protease, MCP-01, produced by a deep-sea psychrotrophic strain of Pseudoaltermonas sp. SM9913 was purified and its autolysis reaction at 20 degreesC-50 degreesC was monitored by capillary electrophoresis. Capillary electrophoresis provides a rapid assay because the degree and state of autolysis of protease MCP-01 could be observed within 6 min. The autolysis rate increased as the temperature rose in the tested range. After 30 min incubation at 30 degreesC, 77% of MCP-01 autolyzed into peptides. However, its activity for the hydrolysis of casein was reduced by only 4%. The rate of loss of activity of MCP-01 was thus slower than that of autolysis of MCP-01 at 30 degreesC. Similar results were obtained when MCP-01 was incubated at 20 degreesC, 40 degreesC and 50 degreesC. Large peptides produced by autolysis of MCP-01 therefore still have catalytic activity. When these large peptides autolyzed further into smaller peptides, the enzyme conformation that retained its catalytic activity was destroyed and activity was lost.