Method for determination of invertase activity in homogenates of human dental plaque

Supragingival human dental plaque was collected from patients with evidence of caries. The plaque was frozen and stored at -20 degrees C. Pooled plaque was homogenized in acetate buffer pH 5.0 in an ice-water bath. By incubating the homogenate at pH 5.0 with [U-14C]-sucrose the formation of glucose and fructose was followed. Incubation in acetate buffer at pH 5.0 eliminated the glycosyltransferase activities and the glycolytic pathway. Normal Michaelis-Menten kinetics were observed until about 40 mM sucrose. At higher concentration of sucrose, excess substrate inhibition occurred. Storage of the homogenate at -20 degrees C resulted in decrease of the invertase activity with time.