The measurement of the cytochrome oxidase activity of enzyme preparations.

containing 1 ml. 15 % glycerol solution, 1-0 ml. 0-1 M-sodium acetate, 0-5 ml. 0-3 M-bicarbonate solution and 0 5 ml. of the enzyme solution. Occurrence of the back reaction would have given rise to an uptake of C02 from the system, but in fact no such uptake was observed. Under these conditions, therefore, no back reaction takes place, so that the incompleteness ofthe de-esterification cannot be due to the existence of an equilibrium between the back and forward reactions. A crude acetone-powder preparation from liver, which contained an active esterase, had no pectinesterase activity when tested by the manometric method. Consequently, liver esterase has no pectinesterase activity under these conditions, although the enzyme preparation from Ps. prunicolca has an esterase action on glycerol esters. This could, however, be due to the presence of esterases in the crude enzyme preparation, although the non-inhibition by diiwopropyl fluorophosphonate does not support this view (see below). Inhibitors. The rate of C02 output remained unchanged in the presence of0.01 M-copper sulphate, potassium cyanide, ferrous sulphate, sodium azide and iodoacetate. A final concentration of 0-0001 Mdiisopropyl fluorophosphonate, which was sufficient to cause 100% inhibition of liver esterase, had a negligible effect on the reaction towards pectin and tributyrin. Tannic acid (0001 M), which is said to inhibit the action of pectinases (Kertesz, 1936), caused no inhibition of the pectin-esterase reaction. The enzyme and pectin solutions were submitted to dialysis against tap water and then distilled water, and the activity determined in the presence and absence of sodium chloride and sodium oxalate, which have been reported as being necessary for activation of the enzyme from tomatoes (Hills & Mottern, 1947). The velocity of the reaction was increased 20% by 0*05 M-sodium chloride, but was unaffected by 0*002 M-oxalate. Further work is being carried out on the pectinase enzymes produced by P8. prunicola, and on the separation of the pectin esterase and pectinase enzymes.