title: An unusual triosephosphate isomerase from the early divergent eukaryote Giardia lamblia.
abstract: Recombinant triosephosphate isomerase from the parasite Giardia lamblia (GlTIM) was characterized and immunolocalized. The enzyme is distributed uniformly throughout the cytoplasm. Size exclusion chromatography of the purified enzyme showed two peaks with molecular weights of 108 and 55 kDa. Under reducing conditions, only the 55-kDa protein was detected. In denaturing gel electrophoresis without dithiothreitol, the enzyme showed two bands with molecular weights of 28 and 50 kDa; with dithiotretitol, only the 28-kDa protein was observed. These data indicate that GlTIM may exist as a tetramer or a dimer and that, in the former, the two dimers are covalently linked by disulfide bonds. The kinetics of the dimer were similar to those of other TIMs. The tetramer exhibited half of the kcat of the dimer without changes in the Km. Studies on the thermal stability and the apparent association constants between monomers showed that the tetramer was slightly more stable than the dimer. This finding suggests the oligomerization is not related to enzyme thermostability as in Thermotoga maritima. Instead, it could be that oligomerization is related to the regulation of catalytic activity in different states of the life cycle of this mesophilic parasite.
authors.affiliation: Laboratorio de Bioquímica-Genética, Instituto Nacional de Pediatría, México, D.F. México.
authors.forename: Gabriel
authors.initials: G
authors.lastname: López-Velázquez
authors.forename: Dora
authors.initials: D
authors.lastname: Molina-Ortiz
authors.forename: Nallely
authors.initials: N
authors.lastname: Cabrera
authors.forename: Gloria
authors.initials: G
authors.lastname: Hernández-Alcántara
authors.forename: Jorge
authors.initials: J
authors.lastname: Peon-Peralta
authors.forename: Lilian
authors.initials: L
authors.lastname: Yépez-Mulia
authors.forename: Ruy
authors.initials: R
authors.lastname: Pérez-Montfort
authors.forename: Horacio
authors.initials: H
authors.lastname: Reyes-Vivas
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D003545:Cysteine / Q000032:analysis; D003593:Cytoplasm / Q000201:enzymology; D004591:Electrophoresis, Polyacrylamide Gel; D004795:Enzyme Stability; D016829:Giardia lamblia / Q000201:enzymology*; D007700:Kinetics; D008969:Molecular Sequence Data; D016415:Sequence Alignment; D013696:Temperature; D014305:Triose-Phosphate Isomerase / Q000032:analysis / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D014305:Triose-Phosphate Isomerase; D003545:Cysteine