Enzyme specificity

Some enzymes are absolutely specific. For example, hydrolysis of urea to ammonia and carbon dioxide is catalyzed by urease. Urea is the only substrate for urease. Thiourea, though structurally similar to urea, will not act as the substrate for urease. Similarly, glucose oxidase will oxidize only beta-D-glucose and no other isomeric form. Thus, these enzymes show absolute specificity. Enzyme activity is expressed as micromoles of substrate conveed to product per minute under specified assay conditions. One standard unit (or International Unit) of enzyme activity (U) is the amount of enzyme that will conve one micromole of substrate per minute per litre of sample and is abbreted as U/L.Ref: DM Vasudevan, page no: 57