Partial purification and characterization of 4-hydroxycinnamic acid:CoA ligase from maize leaves infected with Bipolaris maydis

Anion exchange and hydrophobic interaction chromatography of protein preparations extracted in bulk from maize leaves infected with Bipolaris maydis resulted in over a 600-fold purification of 4-hydroxycinnamic acid:CoA ligase. The native enzyme had an estimated molecular weight of about 51·6 kDa, a value consistent with the range of molecular weights reported for the enzyme isolated from dicotyledonous species. Kinetic analyses of enzyme activities with the various phenylpropanoid substrates demonstrated that there was little preferential substrate specificity among p -coumaric, caffeic, and ferulic acids. The enzyme exhibited no activity when assayed with sinapic acid. Previous reports of CoA ligase isoforms in dicotyledonous species have suggested that the enzyme is involved in the diversion of phenylpropanoids to various biosynthetic pathways. However, no evidence for multiple forms was found in the present investigation, suggesting that the maize CoA ligase is not responsible for metabolic channelling of phenylpropanoids and their distribution within the cell which occur as a response to infection. An alternate interpretation to account for the induction of enzyme activity which occurs in response to infection may be based on activation of phenylpropanoids by UDP-glucosyl transferase.