*Not recognized as an essential nutrient by the AAFCO Dog and Cat Food Nutrient Profiles. (1) One SKB unit is needed to form 10 mg of reducing sugars from 1% starch solution in 30 minutes. (2) One LU liberates the equivalent of one µmol of acid per minute under the conditions of the assay. (3) One CMCU liberates one µmol of reducing sugar per minute under the conditions of the assay. (4) One PU liberates one microgram of tyrosine per hour under the conditions of the assay