EFFECT OF PH ON CO2-ACTIVATED 1-AMINOCYCLOPROPANE-1-CARBOXYLATE OXIDASE ACTIVITY FROM APPLE FRUIT

1-Aminocyclopropane-1-carboxylate(ACC) oxidase, which converts ACC to ethylene, requires CO2 as an activator for its activity, Using crude e xtracts of apple fruit, we examined the effect of pH on CO2-activated ACC oxidase activity. Since gaseous CO2 lowered pH of the assay media, the final pH of the media was either checked after the reaction, or t he pH was maintained by employing CO2-bicarbonate buffer. At ambient C O2, the optimum pH was 7.4; at this pH, maximal activity was attained with 4% atmospheric CO2 as previously reported. As the concentration o f CO2 was increased, the optimum pH gradually shifted toward acidic si de. At 20% CO2, the optimum pH was around 6.7, Thus, the concentration of CO2 to elicit maximal enzyme activity varied greatly with pH. Depe ndence of the enzyme activity on CO2 concentration at various pHs rang ing from 6.0 to 7.5 was investigated. While the affinity of the enzyme for CO2 decreased as the pH decreased, V-max increased as the pH decr eased, reaching a peak activity at pH 6.7. These results indicate that CO2 affects ACC oxidase activity not only by serving directly as an A CC oxidase activator but also by modifying the tissue pH which in turn influences the enzyme activity. Furthermore, some enzyme kinetic para meters for various substrates and CO2 were determined.