Characterization of two isotypes of l-threonine dehydratase from Entamoeba histolytica

Molecular and Biochemical Parasitology
Afzal HusainTomoyoshi Nozaki

Abstract

The genome sequence of the enteric protozoan parasite Entamoeba histolytica suggests that amino acid catabolism plays an important role in energy metabolism. In the present study, we described kinetic and regulatory properties of catabolic l-threonine and l-serine dehydratase (TD) from E. histolytica. TD catalyses the pyridoxal phosphate-dependent dehydrative deamination of l-threonine and l-serine to ammonia and keto acids (2-oxobutyrate and pyruvate, respectively). E. histolytica possesses two TD isotypes (EhTD1-2) showing 38% mutual identity, a calculated molecular mass of 45.0 or 46.5kDa, and an isoelectric point of 6.68 or 5.88, respectively. Only EhTD1 showed l-threonine and l-serine dehydrative deaminating activities whereas EhTD2, in which the amino acid residues involved in the substrate and cofactor binding were not conserved, was devoid of these activities. The k(cat)/K(m) value of EhTD1 was >3 fold higher for l-threonine than l-serine. EhTD1 was inhibited by l-cysteine in a competitive manner with the K(i) values of 1.1mM and 2.2mM for l-serine and l-threonine, respectively. EhTD1 was insensitive to the allosteric activation by AMP or CMP. Three major substitutions of EhTD1 likely attribute to the insensitivity. EhT...Continue Reading

References

Jan 1, 1978·Transactions of the Royal Society of Tropical Medicine and Hygiene·L S DiamondC C Cunnick
Jan 1, 1979·Comparative Biochemistry and Physiology. B, Comparative Biochemistry·T TakeuchiL S Diamond
Jan 19, 1989·Biochimica Et Biophysica Acta·R LeonciniT Keleti
Jul 1, 1995·The Journal of Eukaryotic Microbiology·T Bakker-GrunwaldG Klein
Feb 25, 2005·Nature·Brendan LoftusNeil Hall
Oct 19, 2005·Advances in Parasitology·Tomoyoshi NozakiMasaharu Tokoro
Feb 27, 2007·Trends in Parasitology·Fred R Opperdoes, Graham H Coombs

❮ Previous
Next ❯

Related Concepts

Related Feeds

Amoebiasis

Amoebiasis, infection by the protozoan parasite Entamoeba histolytica, remains a global health problem, despite the availability of effective treatment. Here is the latest research.