کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
5916038 1163355 2008 9 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Biochemical characterization of stage-specific isoforms of aspartate aminotransferases from Trypanosoma cruzi and Trypanosoma brucei
موضوعات مرتبط
علوم زیستی و بیوفناوری بیوشیمی، ژنتیک و زیست شناسی مولکولی زیست شناسی مولکولی
پیش نمایش صفحه اول مقاله
Biochemical characterization of stage-specific isoforms of aspartate aminotransferases from Trypanosoma cruzi and Trypanosoma brucei
چکیده انگلیسی
Three genes encoding putative aspartate aminotransferases (ASATs) were identified in the Trypanosoma cruzi genome. Two of these ASAT genes, presumably corresponding to a cytosolic and mitochondrial isoform, were cloned and expressed as soluble His-tagged proteins in Escherichia coli. The specific activities determined for both T. cruzi isozymes were notably higher than the values previously reported for Trypanosoma brucei orthologues. To confirm these differences, T. brucei mASAT and cASAT were also expressed as His-tagged enzymes. The kinetic analysis showed that the catalytic parameters of the new recombinant T. brucei ASATs were very similar to those determined for T. cruzi orthologues. The cASATs from both parasites displayed equally broad substrate specificities, while mASATs were highly specific towards aspartate/2-oxoglutarate. The subcellular localization of the mASAT was confirmed by digitonin extraction of intact epimastigotes. At the protein level, cASAT is constitutively expressed in T. brucei, whereas mASAT is down-regulated in the bloodstream forms. By contrast in T. cruzi, mASAT is expressed along the whole life cycle, whereas cASAT is specifically induced in the mammalian stages. Similarly, the expression of malate dehydrogenases (MDHs) is developmentally regulated in T. cruzi: while glycosomal MDH is only expressed in epimastigotes and mitochondrial MDH is present in the insect and mammalian stages. Taken together, these findings provide evidence for a metabolically active mitochondrion in the mammalian stages of T. cruzi, and suggest that the succinate excreted by amastigotes more likely represents a side product of an at least partially operative Krebs cycle, than an end product of glycosomal catabolism.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Molecular and Biochemical Parasitology - Volume 161, Issue 1, September 2008, Pages 12-20
نویسندگان
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