Control by pH of Cell Wall Peroxidase Activity Involved in Lignification

pH affected both conyferyl alcohol (CA) oxidation and NADH-dependentH₂O₂ formation catalysed by cell wall-bound peroxidase fromlupin. The kinetics of CA oxidation shown at pH 5.0 was of theMichaelian-type, independently of the physical state (boundor soluble) of the enzyme in the cell wall, whereas at pH 8.0,it was cooperative. The affinity of the enzyme to H₂O₂and therate of H₂O₂ formation were higher at pH 8.0 than at pH 5.0.The kinetics of H₂O₂ formation at pH 8.0 was strongly cooperative.These results are discussed with respect to the important roleof pH in the regulation of cell wall peroxidase activities involvedin lignification. (Received December 12, 1988; Accepted December 7, 1988)