Carbon Dioxide Fixation into Oxalacetate in Higher Plants.

Abstract

of this Wood-WVerkman It was recognized early that simple addition of CO2 to pyruvate occurred with such an unfavorable free energy change that some device for supplying chemical energy was essential if the reaction was to play a quantitatively important role in intermediary metabolism (7). Three different C02-fixing processes whereby this end can be achieved have been described to date. These are: a) the enzyme (or Ochoa) reaction, b) the phosphoenolpyruvate carboxykinase (or pepearboxykinase) reaction, and c) the phosphoenolpyruvate carboxylase (or pepearboxylase) reaction. All of these reactions involve the addition of CO2 to a C-3 unit, to form a C-4 dicarboxylic acid; and all three reactions must be combined with some other reaction to give the net result shown in equation (1). The focus of current interest has been partially on the detailed mechanism of these different enzvme reactions, and partially on their physiological interrelationships. Although the malic enzyme had been shown to be widely distributed (24), only limited information was available about the distribution of the other enzymes. The work described in the present paper was concerned mainly with the problems of assaying pepearboxylase and pepearboxykinase, and determining their reaction characteristics and distribution in higher plants. The reaction catalyzed by pepearboxykinase, first described by Bandurski and Greiner (3, 4), is shown in equation (2). The pepcarboxykinase reaction was first clearly defined by Utter and Kurahashi (22, 23), who showed that the enzyme from bird liver catalyzed the reaction shown in equation (3).