Enzyme unit many kinds of substance besides enzymes (for example, vitamins and hormones). Enzyme unit The enzyme unit (symbol U or sometimes EU) is a unit for the amount of a particular enzyme. One U is defined as the amount of the enzyme that produces a certain amount of enzymatic activity, that is, the amount that catalyzes the conversion of 1 micro-mole of substrate per minute. The conditions also have to be specified: one usually takes a temperature of 25°C and the pH value and substrate concentration that yield the maximal substrate conversion rate. The enzyme unit was adopted by the International
Action (physics) in time and space. Action has the dimensions of [energy]⋅[time], and its SI unit is joule-second, which is identical to the unit of angular momentum. In classical physics, the term "action" has a number of meanings. Most commonly, the term is used for a functional formula_2 which takes a function of time and (for fields) space as input and returns a scalar. In classical mechanics, the input function is the evolution q("t") of the system between two times "t" and "t", where q represents the generalized coordinates. The action formula_3 is defined as the integral of the Lagrangian "L" for