The enzyme Trehalase is a glycoside hydrolase, produced by cells in the brush border of the small intestine, which catalyzes the conversion of trehalose to glucose. It is found in most animals. The non-reducing disaccharide trehalose (α-D-glucopyranosyl-1,1-α-D-glucopyranoside) is one of the most important storage carbohydrates, and is produced by almost all forms of life except mammals. The disaccharide is hydrolyzed into two molecules of glucose by the enzyme trehalase. There are two types of trehalases found in Saccharomyces cerevisiae, viz. neutral trehalase (NT) and acid trehalase (AT) classified according to their pH optima [4]. NT has an optimum pH of 7.0, while that of AT is 4.5. Recently it has been reported that more than 90% of total AT activity in S. cerevisiae is extracellular and cleaves extracellular trehalose into glucose in the periplasmic space. Trehalose hydrolysis One molecule of trehalose is hydrolyzed to two molecules of glucose by the enzyme trehalase. Enzymatic hydrolysis of trehalose was first observed in Aspergillus niger by Bourquelot in 1893. Fischer reported this reaction in S. cerevisiae in 1895. Since then the trehalose hydrolyzing enzyme, trehalase (α, α-trehalose-1-C-glucohydrolase, EC 3.2.1.28) has been reported from many other organisms including plants and animals. Though trehalose is not known to be produced by mammals, trehalase enzyme is found to be present in the kidney brush border membrane and the intestinal villi membranes. In the intestine the function of this enzyme is to hydrolyze ingested trehalose. Individuals with a defect in their intestinal trehalase have diarrhea when they eat foods with high trehalose content, such as mushrooms. Trehalose hydrolysis by trehalase enzyme is an important physiological process for various organisms, such as fungal spore germination, insect flight, and the resumption of growth in resting cells. Bacterial trehalase Trehalose has been reported to be present as a storage carbohydrate in Pseudomonas, Bacillus, Rhizobium and in several actinomycetes and may be partially responsible for their resistance properties. Most of the trehalase enzymes isolated from bacteria have as optimum pH of 6.5–7.5. The trehalase enzyme of Mycobacterium smegmatis is a membrane bound protein. Periplasmic trehalase of Escherichia coli K12 is induced by growth at high osmolarity. The hydrolysis of trehalose into glucose takes place in the periplasm, and the glucose is then transported into the bacterial cell. Another cytoplasmic trehalase has also been reported from E. coli. The gene, which encodes this cytoplasmic trehalase, exhibits high homology to the periplasmic trehalase.