Maltose utilization by extracellular hydrolysis followed by glucose transport in Trichomonas vaginalis

Abstract

The amitochondriate parasitic protist Trichomonas vaginalis can utilize either glucose or maltose as carbon and energy source. The mechanisms of maltose utilization were explored with uptake experiments using radio-isotope labelled maltose in combination with the silicone-oil centrifugation technique and enzymatic assays measuring maltose hydrolysis. The uptake of maltose label became saturated after 2-3 h. The uptake of maltose as a function of the external maltose concentration was linear at low concentrations with no further increase at higher levels, kinetics characteristic of reactions obeying Michaelis-Menten kinetics preceded by a diffusion-limited step. Increased viscosity of the medium resulted in decreased maltose uptake, indicating an extracellular location of the diffusion-limited step. Most of the cellular alpha-glucosidase activity of T. vaginalis was detected on the cell surface, suggesting that maltose is hydrolysed to glucose outside the cell. Glucose interfered more with maltose uptake, and maltose less with glucose uptake, than would be expected if 1 mol of maltose were the equivalent of 2 mol of glucose. This pattern of interaction indicated that the interference occurs before the common metabolic pathway and even before the transport step, supporting the idea of extracellular maltose hydrolysis. We conclude that maltose is hydrolysed to glucose in the boundary layer of the cell, a process akin to membrane digestion in vertebrate enterocytes and on the teguments of helminths. The glucose formed is then transported by the glucose carrier of the organism.

Adaptation of the carbon metabolism of Trichomonas vaginalis to the nature and availability of the carbon source

“…The step catalysed by hexokinase or glucokinase, phosphorylation of glucose to glucose 6-phosphate, is irreversible. mginalis is controlled by glucokinase, and, in the case of maltose metabolism, whether the a-glucosidase that hydrolyses maltose extracellularly to form glucose (Ter Kuile & Muller, 1994) exerts most flux control.…”

“…The first step in the uptake and metabolism of maltose is its hydrolysis to form two molecules of glucose, a reaction catalysed by an ectoenzyme located at the cell surface (Ter Kuile & Muller, 1994). The glucose thus formed can then no longer be distinguished from glucose already present in the medium.…”

“…The mechanism for glucose transport across the plasma membrane in T. vaginalis is facilitated diffusion (Ter I<uile & hi uller, 1993). Maltose is hydrolysed extracellularly by an a-glucosidase and the glucose formed is then taken up (Ter Kuile & Muller, 1994). In culture T. vaginalis can reach division times of 4 h, but in the urogenital tract, gronth is estimated to be much slower.…”

Expression and characterization of a β-fructofuranosidase from the parasitic protist Trichomonas vaginalis

“…Growth using maltose as a carbon source has been especially well studied in T. vaginalis [13,14]. Work by ter Kuile showed that the organism expresses cell-associated maltase activity that cleaves maltose to yield two molecules of glucose, which are then transported into the cell [14,15].…”

Involvement of the GP63 protease in infection of Trichomonas vaginalis

“…T. vaginalis lives as a parasite and utilizes nutrients from its host for survival, which is considered to be the ultimate consequence of pathogenesis. It hydrolyzes organic components from the mucus and extracellular matrix of its host cells into glucose, which is then transported into the parasitic cells (Asami and Nakamura 1955;ter Kuile and Muller 1995) where nucleotides from the host are used for DNA synthesis (Gonzalez-Lazaro et al 2005). We assume that cell surface proteins are probably critical for preliminary interactions between parasites and mucosa/extracellular matrices and thus may be related to subsequent cytotoxicity.…”