The pool sizes of the common amino acids in purified intact chloroplasts from Vicia faba L. were measured (nanomoles per milligram chlorophyll). The three amino acids present in the highest concentrations were glutamate, aspartate, and threonine. Alanine, serine, and glycine were each present at levels between 15 and 20 nanomoles per milligram chlorophyll and 13 other amino acids were detectable at levels below 10.Only aspartate, alanine, glycine, serine, threonine, and lysine became labeled during photosynthetic "CO2 fixation by isolated chloroplasts: the label in aspartate represented over 60 % of the total '4C found in the amino acids. Glutamate dehydrogenase, glutamate-oxaloacetate, and glutamate-pyruvate aminotransferases were present in the chloroplasts, but no other trans. ferase activities from glutamate could be detected. The chloroplasts were able to synthesize a total of 17 other protein amino acids from either alanine or aspartate, but no synthesis of leucine by aminotransferase reactions could be detected. The synthesis of aspartate was studied in more detail. The enzyme systems required for the generation of oxaloacetate from triose phosphate were virtually absent from the chloroplasts but present in the leaf cytoplasmic fraction. Addition of either a leaf "cytoplasmic" fraction or an oxaloacetate generating system resulted in an increased proportion of the total "C fixed being found in the amino acid fraction during photosynthetic "CO2 fixation.It is suggested that the supply of oxaloacetate from the cytoplasm is one of the important factors controlling the synthesis of amino acids by the chloroplast.During "CO2 fixation in photosynthesizing algal cells (2,6,32) 2-ketoglutarate and that both the synthesis of glutamate and of alanine and aspartate probably take place within the chloroplast. An L-glutamate dehydrogenase would be able to catalyze the reductive amination of 2-ketoglutarate. Isolated chloroplasts have been shown to possess such an enzyme dependent on reduced pyridine nucleotides (23, 30) and are capable of catalyzing the photoreduction of 2-ketoglutarate to glutamate (30, 11). The recorded rates of photoreduction of 2-ketoglutarate by isolated chloroplasts are 0.4 ,umole/mg chl-hr (spinach [35]) and 0.6 ,umole/mg chl-hr (broad bean [11]). These low rates may partly account for the finding that, although chloroplasts can now be prepared which are capable of photosynthetic CO2 fixation at rates comparable with those observed in vivo (7,17,18), in general only 5 to 10% of the total radioactivity is recovered in the amino acid fraction (9,37). In isolated chloroplast suspensions aspartate (37), aspartate and alanine (9, 25), and glycine and serine (8) have been shown to be among the products of photosynthetic "CO2 fixation.Assuming the initial incorporation of ammonia in the chloroplast is into glutamate, a further question arises concerning the mode of transfer of the amino group from glutamate to the other amino acids. Amino transferase systems would provide a possible mechanism...

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A method is described for the preparation of catalase particles from homogenates made from suspensions of epithelial cells of the small intestine of the guinea pig. Electron microscope examination of the preparations revealed the presence of small diaminobenzidine-positive particles measuring 0.1–0.3 nm in diameter and resembling the microperoxisomes observed by Novikoff and Novikoff (1972. J. Cell Biol. 53:532.). Analytical data upon which the method is based are presented. The technique consisted of a rate zonal separation of microperoxisomes from large particles followed by an isopycnic separation from less dense organelles. Application of the method yielded microperoxisomes purified between 20- and 30-fold.