Abstract
A phenoloxidase from spinach leaves was extensively purified to homogeneity. The molecular weight of the purified enzyme was 150, 000 by gel filtration, and 40, 000 by SDS-polyacrylamide gel electrophoresis. The enzyme contained 2 atoms of copper per 150, 000 of molecular weight. The optimum pH of the enzyme action is near 6.5. The enzyme lacks cresolase activity. Km and k0 were measured for some 4-substituted catechols and oxygen. Log k0 values for catechols substituted in position 4 by -NO2, -CHO, -CH3, -COOH, or -CH2CH2COOH were confirmed to fit Hammett relationships (ρ-Values for σp and σm are - 3.652 and - 4.007, respectively), but not for log Km values. Log(k0/Km) values for the same substrates were confirmed to have this relationship, but protocatechuic and hydrocaffeic acids deviated from this linearity.
