The p-coumaryl CoA ligase of potato tubers

The demonstration of activity of p-coumaryl CoA ligase in extracts of aged potato disks proved difficult owing to the presence of extremely high levels of apyrase which caused rapid hydrolysis of ATP, a co-factor for ligase activity. This problem was largely overcome by including an inhibitor of apyrase, sodium fluoride in the ligase assay and by initiation of the reaction with ATP. A method for the separation of apyrase and p-coumaryl CoA ligase by chromatography on DEAE-cellulose is described. p-Coumaryl CoA ligase was not detectable in freshly prepared disks of potato tubers. However on ageing in the light a large increase in the activity of this enzyme occurs, The enzyme of aged potato disks shows high activity with p-coumaric, ferulic, caffeic and with m- and p-methoxycinnamic acids. However the affinity of the enzyme for the methoxy derivatives is much lower than for cinnamic acids bearing free hydroxyl groups.