CO2-Fixing Enzymes

CO₂ fixation by the nervous system has been demonstrated with the use of ¹⁴ C-labeled bicarbonate in the retina (Crane and Ball, 1951), in the brain of 1-d-old mice (Moldave et al., 1953), and in the adult cat brain (Berl et al., 1962a,b). When cat brain was perfused with labeled bicarbonate and the specific radioactivity of ¹⁴ CO₂ was maintained at a constant level, most of the radioactivity fixed in the brain was found in free aspartate, glutamate, and glutamine, with a small amount in lactate (Berl et al., 1962a,b; Otsuki et al., 1963; Waelsch et al., 1964). Aspartate had the highest specific radioactivity, which approached about 10% of that of infused radioactive bicarbonate. When ammonia was administered together with H¹⁴ CO₃ ^- to cats, the total amount of ¹⁴ CO₂ -fixation