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
Barn (unit) of a nucleus with an electric field gradient. While the barn is not an SI unit, the SI standards body acknowledges its existence due to its continued use in particle physics. The etymology of the unit barn is whimsical: during Manhattan Project research on the atomic bomb during World War II, American physicists at Purdue University needed a secretive unit to describe the approximate cross sectional area presented by the typical nucleus (10 m) and decided on "barn". This was particularly applicable because they considered this a large target for particle accelerators that needed to have direct strikes on nuclei