Enzymes are highly selective for compounds that bind into the active site and are converted to product. Therefore, specificity depends on how tightly the enzyme binds a compound and how rapidly it converts the compound to product. Quantitatively, specificity is measured by V max/Km , where V max is best expressed as rate per mole of enzyme. The higher the value V max/Km , called the specificity coefficient, the more specific the enzyme is for a substrate.