Sucrose Synthetase in the Latex ofHevea brasiliensisMuell. Arg

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Abstract
Sucrose synthetase (EC 2.4.1.13) was found in the latex of the rubber tree but the activity of sucrose phosphate synthetase (EC 2.4.1.14) was not detected. The enzyme was purified and some properties have been investigated. Examination of the kinetics of sucrose synthesis revealed Km of 0.56 mM for uridine diphosphoglucose and 3.85 mM for fructose. Mg2+ and cyanide activated sucrose synthesis but reduced the cleavage reaction. Increased pH had the same effect, the synthetic activity being higher than the activity of sucrose breakdown within the physiological levels of latex pH. In the latex of regularly tapped trees, the total enzyme activity in the direction of synthesis was about 10% or less of the total invertase activity at pH 7.0. Because of the strong limitation of invertase under natural conditions, the proportion of actual synthetase activity is, however, much higher and evidence is presented that in the latex of regularly tapped trees this activity significantly reduces carbohydrate breakdown. Some indications have been obtained that this involvement of sucrose synthetase is weakened by application of Ethrel to the bark. A reduction of its synthetic activity, accompanied by an acceleration of sucrose utilization in latex cytoplasm and by an increase of latex yield, could be observed before the treatment-induced rise of pH enhancing inver.