The enzymatic characteristics of peroxisomes of amphibian and avian liver and kidney.

Peroxisomes have been identified on the basis of morphological criteria in a variety of species (Hruban and Rechcigl, 1969). Biochemical characterization, however, has been limited to rat liver (deDuve & Baudhuin, 1966; Leighton, et al., 1968), rat kidney (Allen et al., 1965; deDuve & Baudhuin, 1966), Tetrahymena pyriformis (Baudhuin et al., 1965b; Miiller et al., 1968), Acanrhoamoeba (Miiller and Moller, 1967), germinating castor beans (Breidenbach et al., 1968), and the leaves of several plants (Tolbert et al., 1968a; Tolbert et al., 1968b). In germinating castor beans the peroxisome contains the enzymes of the glyoxylate cycle and, thus, may function in glyconeogenesis (Breidenbach et al., 1968). The peroxisome in leaf tissue contains glycolate oxidase and NADH-glyoxylate reductase and may function in photorespiration (Tolbert et al., 1968a; Tolbert et al., 1968b). In Tetrahymena, remnants of the glyoxylate cycle are present (isocitrate lyase and malate synthetase) (Miiller et al., 19681, while in higher animals the components of the cycle appear to be absent. In these latter groups, the peroxisome appears to be limited in its enzymatic composition to. catalase, D-amino acid oxidase, a-hydroxy acid oxidase, and urate oxidase (in rat liver but not in rat kidney) (deDuve & Baudhuin, 1966). In these cases it is difficult to define any unified metabolic role for peroxisomes, although it has been suggested that they may participate in coupled peroxidatic reactions, or in the regeneration of nicotinamide adenine dinucleotide (NAD) from reduced NAD, or in the production of keto-acids that may be utilized in fatty acid synthesis (deDuve & Baudhuin, 1966). Our attention has been directed toward the possible significance of urate oxidase in the peroxisomes of some species. This enzyme is a participant in the sequence of enzymes responsible for the degradation of purines. This sequence, in its complete form (FIGURE l ) , leads to the formation of glyoxylate and urea, the latter ultimately being hydrolyzed to carbon dioxide and ammonia in certain groups (Brown et al., 1966). It has been suggested that the glyoxylate formed through the action of this sequence may be aminated and subsequently incorporated into purine, thus constituting a purine cycle (Brown et al., 1966). The extent to which this cycle generally exists is unknown. The purine catabolic sequence is of further interest in that it has been subject to considerable evolutionary modification (FIGURE 1) (Baldwin, 1964) and might be expected to furnish clues to the evolution of a particle containing its components. We have undertaken a preliminary survey of the association of