Polyphenol oxidase (PPO) was isolated from grapes grown in Spain and its characteristics were studied. The partially purified enzyme had both cresolase and catecholase activities. Catecholase activity had a pH optimum in a range 3.5–4.5 and was characterized by a relatively high stability to heat. The apparent K M for 4‐methylcatechol was 9.5 mM. Cresolase activity presents a lag period which is modulated by different factors: enzyme concentration, substrate concentration, temperature or pH. The presence of o‐diphenols in the reaction medium abolishes the lag period, these acting as co‐substrates. The apparent K M towards p‐cresol and the activation constant for o‐diphenol for cresolase activity were 0.35 mM and 1.75 μM, respectively.
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Valero et al. (1988) studied this question.
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