Distribution of C14 in Serine and Glycine after C14O2 Photosynthesis by Isolated Chloroplasts. Modification of Serine-C14 Degradation

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...

Section: Introductionmentioning

confidence: 97%

mentioning

confidence: 97%

Amino Acid Biosynthesis by Isolated Chloroplasts during Photosynthesis

Kirk

Leech

1972

“…Glycolate-2-14C and phosphoglycolate-2-14C were purchased from Nuclear Research Chemicals, Orlando, Florida, and were determined by tus on 2 dimensional paper chromatograms (4) to be chromatographically pure. The photosynthetic experiments with '4CO., the isolation of the '"C produicts, and the degradation procedtures for 3-P-glycerate, glycine glycolate and serine have been described elsewhere (8,12,42 (14,19,39) (12,14,19 (39), and the stuggestion b)y Smith et al…”

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confidence: 99%

Glycolate Pathway in Algae

Hess¹,

Tolbert²

1967

Self Cite

102

For several reasonis it has been assuimed that algae also containe(d a glycolate pathway similar to that in the higher plant. Algae rapi(dly labeled glycolate, glycine, andl serinie (duiring ' 4C().0 photosynthesis (3,5,21). Fuirther, it has beeni reporte(d that glycolate-'4C was converted by .Scnedes)m(s to glycinie ainl(d serinie (24 ). It was kniowni that higher planits, rapidly, conlvert glycolate-1-'4C to hoth glycinie-1-14C and( serine-I-14C ani(l conivert glycolate-2-'C to glycine-2-14C andl serine-2, 3-'I4C (22,31,34, 35

“…This procedure is similar to Sakami's procedure (28) for the degradation of serine, which has been somewhat modified here (5). Mesotartrate was degraded by two similar procedures.…”

mentioning

confidence: 99%

Excretion of Glycolate, Mesotartrate and Isocitrate Lactone by Synchronized Cultures of Ankistrodesmus braunii

Chang

Tolbert

1970

Self Cite

Algae excrete numerous organic compounds, and in 1956 (38) glycolate was identified as the major component which is now recognized as excreted by most algae (12,14,17,20,26) and perhaps chloroplasts (37). Currently glycolate excretion is attributed to the repression by CO2 (21) rapidly growing Chlorella cultures excreted glycolate; Allen (1) claimed that the amount of excretion by Chiamydomonas paralleled growth; but Forsberg et al. (7) stated that organic compounds were excreted during phases of declining relative growth rates and in the stationary phase. In a preliminary report of this work (4), it was shown that young growing cells were most active for glycolate excretion, and these results have been confirmed (8).Except for glycolate, the excretion of other acids and compounds seems to be specific for certain algae. Excreted