Pectinesterase reactions catalyzed

Figure 4. Initial speed of the pectin hydrolysis reaction catalyzed by pectinesterase 1 — theoretically calculated symmetric bell, 2 — experimentally obtained curve.

Maximal speed (Vmax) and supposed Michaelis constant (K ) of pectin hydrolysis reaction (catalyzed by the studied pectinesterase) were determined in Zinewedwer — Berk coordinated, They were determined in the range of substrate concentration values that was below optimum one V = 14.7 10 M min K = 5.56 10 M. The value of dissociated constant (KJ of the triple enzyme—substrate complex was determined from the experimental data at high substrate concentration. It was the following Kj= 0.22 M. Bunting and Murphy method was used for determination. 

Kinetic parameters of the reaction of pectin hydrolysis (catalyzed by analyzed pectinesterase) were obtained by Zineweaver—Berk method [12]. 

It was found out that reaction of the hydrolysis of highlymetoxilated beet pectin (catalyzed by P. fellutanum pectinesterase) obeyed Michaelis—Menten equation only under low substrate concentrations (up to 1.2%), when graph of the dependence of reaction speed was hyperbolic in form. 

Pectinesterase and limonin D-ring lactonase are the only enzymes known to catalyze reactions that adversely affect the quality of citrus juices. Bruemmer et al. (64) listed other enzymes that have been detected in citrus juices and described some of the reactions that can occur in the juices. None of the reactions appear to noticeably affect the quality of commercial juices. Freshly extracted citrus juices contain esterase (EC 3.1.1.1) (65, 66) and phosphatase (EC 3.1.32) (66, 67) activities. Native substrates in orange juice for peroxidase... 

Other pectins with degree of esterification of about 10, 30 and 40% (Table I) were obtained by enzymic deesterification of the initial preparation. An orange pectinesterase was used and the pH of the reaction was 6 in order to avoid concurrent base-catalyzed saponification. The action of plant pectinesterase is known (16-18) to result in a blockwise arrangement of free carboxyl groups in the pectic molecules. The enzymic preparation does not contain depolymerase activities as shown by the constancy of the intrinsic... 

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