phenolase/spinacia

1. The conditions under which oxygen consumption in excess of that required for the hydroxylation of p-coumaric acid to caffeic acid, catalysed by spinach-beet phenolase, can be suppressed, have been examined. 2. With dimethyltetrahydropteridine as electron donor, oxygen uptake was exactly

1. Under defined conditions, the hydroxylation of p-coumaric acid catalysed by a phenolase from leaves of spinach beet (Beta vulgaris L.) was observed to develop its maximum rate only after a lag period. 2. By decreasing the reaction rate with lower enzyme concentrations or by increasing it with

Treatment of spinach-beet phenolase with H2O2 under aerobic conditions results in a stimulation of the p-coumaric acid hydroxylation it catalyses, but not the caffeic acid oxidation. Spectroscopic evidence suggests that an oxygenated enzyme species is formed under these conditions.

1. A spectrophotometric assay is described that enables the hydroxylation of p-coumaric acid to caffeic acid, catalysed by spinach-beet phenolase, to be followed continuously. 2. Initial-velocity and inhibitor studies indicate that the order of substrate addition is oxygen, p-coumaric acid and

1. Chloroplasts isolated from leaves of spinach-beet (Beta vulgaris L. ssp. vulgaris) do not catalyse the hydroxylation of p-coumaric acid in the dark unless a reductant (such as ascorbate, NADH or NADPH) is added. Superoxide dismutase has no effect on this reaction. 2. Illuminated chloroplasts

1. An enzyme from the leaves of spinach beet (Beta vulgaris L.) that catalyses the hydroxylation of p-coumaric acid to caffeic acid in the presence of ascorbate has been purified about 1000-fold on a protein basis. 2. It is activated by high concentrations of ammonium sulphate and sodium chloride.