ABSTRACT
Pyruvate carboxylase (EC 6.4.1.1) is a biotin containing mitochondrial enzyme, which catalyzes the conversion of pyruvate to oxalacetate by CO2 fixation (Figure 48.1) [1,2]. As in the case of other carboxylases the reaction mechanism is a twostep process in which biotin is first carboxylated and then the carboxyl group is transferred to the acceptor, pyruvate [3,4]. There is a separate catalytic site for each of the two steps. The enzyme is a tetramer of 500 kD whose individual equal-sized protomers have a different structure from other biotincontaining carboxylases [5], but the highly conserved amino acid sequence at the biotin site of biotin-containing carboxylases, Ala-Met-Lys-Met is present in pyruvate carboxylase [6]. The biotin is linked to the amino group of the lysine.
