| Abstrakt: |
It is true1that crystalline trypsin2can clot ordinary citrated plasma and can activate prothrombin without added calcium. As these experimental facts appear to conflict with the statement of Northrop and Kunitz3that a trace of ionized calcium is necessary, we have reinvestigated the point minutely, with an enzyme preparation kindly supplied by the Rockefeller workers.It was found (Table I) that the trypsin is much more active in the presence of added calcium salt and that excess of citrate can inhibit its action. Whereas trypsin alone requires amounts of the order of 1-2 mg to coagulate 1 cc of citrated dog plasma and the clots quickly undergo fibrinolysis, much smaller quantities (0.01-0.02 mg) of enzyme, synergized by calcium, produce better clots which do not lyse in 24-48 hours.The addition of cephalin to clotting systems containing the proteolytic enzyme results in a minor improvement of the thrombic activity developed. For its full demonstration, this requires the presence of calcium.A minor loss of activity on boiling the crystalline trypsin solution4is restored by added cephalin and calcium. It is known, of course, that cruder enzyme preparations are thermolabile.Lung extracts evince a thromboplastic action exactly analogous to that of dilute trypsin (pluscephalin). The partial retention of the activity in boiled lung extract has been explained on the basis of its phospholipid content.5We have a semi-quantitative confirmation of this in tests made with the isolated (total) lung P-lipids. Pending isolation, may we not regard the major, thermolabile factor in thromboplastic tissue extracts as analogous to a weak proteolytic enzyme? |
