title: Hysteresis and positive cooperativity as possible regulatory mechanisms of Trypanosoma cruzi hexokinase activity.
abstract: In Trypanosoma cruzi, the causal agent of Chagas disease, the first six or seven steps of glycolysis are compartmentalized in glycosomes, which are authentic but specialized peroxisomes. Hexokinase (HK), the first enzyme in the glycolytic pathway, has been an important research object, particularly as a potential drug target. Here we present the results of a specific kinetics study of the native HK from T. cruzi epimastigotes; a sigmoidal behavior was apparent when the velocity of the reaction was determined as a function of the concentration of its substrates, glucose and ATP. This behavior was only observed at low enzyme concentration, while at high concentration classical Michaelis-Menten kinetics was displayed. The progress curve of the enzyme's activity displays a lag phase of which the length is dependent on the protein concentration, suggesting that HK is a hysteretic enzyme. The hysteretic behavior may be attributed to slow changes in the conformation of T. cruzi HK as a response to variations of glucose and ATP concentrations in the glycosomal matrix. Variations in HK's substrate concentrations within the glycosomes may be due to variations in the trypanosome's environment. The hysteretic and cooperative behavior of the enzyme may be a form of regulation by which the parasite can more readily adapt to these environmental changes, occurring within each of its hosts, or during the early phase of transition to a new host.
authors: Laboratorio de Enzimología de Parásitos, Departamento de Biología, Facultad de Ciencias, Universidad de Los Andes, Mérida 5101, Venezuela. Electronic address: hectoracosta@ula.ve.
authors: Héctor
authors: H
authors: Acosta
authors: Laboratorio de Enzimología de Parásitos, Departamento de Biología, Facultad de Ciencias, Universidad de Los Andes, Mérida 5101, Venezuela.
authors: Ana
authors: A
authors: Cáceres
authors: Instituto Venezolano de Investigaciones Científicas, Caracas 1020, Venezuela.
authors: Eglys
authors: E
authors: González-Marcano
authors: Laboratorio de Enzimología de Parásitos, Departamento de Biología, Facultad de Ciencias, Universidad de Los Andes, Mérida 5101, Venezuela.
authors: Wilfredo
authors: W
authors: Quiñones
authors: Laboratorio de Fisiología Animal, Departamento de Biología, Facultad de Ciencias, Universidad de Los Andes, Mérida 5101, Venezuela.
authors: Luisana
authors: L
authors: Avilán
authors: Laboratorio de Enzimología de Parásitos, Departamento de Biología, Facultad de Ciencias, Universidad de Los Andes, Mérida 5101, Venezuela.
authors: Michel
authors: M
authors: Dubourdieu
authors: Laboratorio de Enzimología de Parásitos, Departamento de Biología, Facultad de Ciencias, Universidad de Los Andes, Mérida 5101, Venezuela.
authors: Juan Luis
authors: JL
authors: Concepción
mesh_terms: D000222:Adaptation, Physiological; D000255:Adenosine Triphosphate / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D005947:Glucose / Q000378:metabolism; D006019:Glycolysis; D006593:Hexokinase / Q000378:metabolism*; D007700:Kinetics; D014349:Trypanosoma cruzi / Q000201:enzymology* / Q000378:metabolism
chemical_list: D000255:Adenosine Triphosphate; D006593:Hexokinase; D005947:Glucose
keywords: Cooperativity; Glycosome; Hexokinase; Hysteresis; Trypanosoma cruzi