Patterns of Methionine and Lysine Biosynthesis in the Trypanosomatidae During Growth*

Abstract

SYNOPSIS. Nine Crithidia spp., 2 Blastocrithidia spp., 3 Leptomonas spp. and 2 Trypanosoma spp. were tested for ability to synthesize methionine and lysine during growth. A prerequisite for methionine biosynthesis is an inordinately high level of folic acid (0.1 mg/100 ml) in the medium. Crithidia factor‐type unconjugated pteridines cannot spare this requirement. Since the methionine‐synthesis factor is still present after acid hydrolysis which destroys folic acid, the factor is either a breakdown product of folic acid or an impurity in the commercial product. All save C. fasciculata var. noelleri and C. from Syrphid could synthesize methionine from homocysteine thiolactone. None of the organisms synthesized lysine from α‐aminoadipic acid (AAA), thus ruling out the existence of the AAA pathway for lysine synthesis in the Trypanosomatidae. Nine of the organisms synthesized lysine from a mixture of LL‐ and meso‐α,e‐diaminopimelic acid. Since both LL‐ and meso‐DAP are intermediates in the biosynthesis of lysine by the DAP pathway (LL‐DAP→meso‐DAP→lysine) and since decarboxylation of either LL‐ or meso‐DAP could result in formation of lysine, pure meso‐DAP was tested and found active. Thus at least the terminal portion of the DAP pathway for lysine synthesis exists in these true animal cells. Statements about absence of ability to synthesize lysine in animal cells and consequent evolutionary interpretations will therefore require revision.

Endosymbiosis in trypanosomatids: the genomic cooperation between bacterium and host in the synthesis of essential amino acids is heavily influenced by multiple horizontal gene transfers

“…However, experimental evidence has shown that homocysteine and/or cystathionine could substitute for methionine in culture media for trypanosomatids [43,45,64]. …”

“…Methionine is included in all defined media designed for the growth of trypanosomatids with or without symbionts [ 20 , 22 , 43 ], suggesting that these protozoans are incapable of methionine synthesis. However, experimental evidence has shown that homocysteine and/or cystathionine could substitute for methionine in culture media for trypanosomatids [ 43 , 45 , 64 ].…”

The Uptake and Metabolism of Amino Acids, and Their Unique Role in the Biology of Pathogenic Trypanosomatids

“…Trypanosomatids are unable to synthesize Lys and rely on uptake to obtain this amino acid [ 52 , 90 , 91 ]. Accordingly, Lys has been shown to be essential for cell growth in Leishmania [ 85 ].…”

“… a T. brucei is auxotrophic for Pro [ 39 ], b TriTryps are auxotrophic for branched-chain amino acids [ 83 , 84 , 85 ], c TriTryps are auxotrophic for Arg [ 85 , 86 ], d T. brucei and T. cruzi are auxotrophic for Orn [ 2 , 87 , 88 , 89 ], e T. cruzi is auxotrophic for His [ 61 , 86 ], f TriTryps are auxotrophic for Lys [ 52 , 90 , 91 ]. …”

Electrophoretic Analysis of Endonuclease‐Generated Fragments of k‐DNA, of Esterase Isoenzymes, and of Surface Proteins as Aids for Species Identification of Insect Trypanosomatids1

“…Awareness of these difficulties has stimulated the search for other criteria of biological (33,(47)(48)(49), nutritional (9,10,17,19,34,42,43,60), immunological (2,12,32,42,52,53) or bio-' This investigation was supported by funds from Conselho Nacional de Pesquisas to E. P. Camargo chemical nature that could be of use as additional aids for species separation of lower trypanosomatids. Biochemical methods, although largely used for the characterization of species and strains of heteroxenous trypanosomatids ( I , 7, 24, 30, 35, 37, 40, 41) have been used for comparative purposes among monoxenic trypanosomatids only in a few instances (4,5,12,13,15,18,20,21,27,34,54,58,61).…”