transferase

Meaning: A transferase is an enzyme that moves a functional group from a donor molecule to an acceptor molecule. It is one of the six MCAT enzyme classes (oxidoreductases, transferases, hydrolases, lyases, isomerases, ligases). Groups moved include phosphoryl, amino, methyl and acyl. Examples: kinases (phosphate from ATP to a substrate) and aminotransferases (amino group from an amino acid to an α-keto acid).

Equation: D–X + A → D + A–X, where D is the donor, A is the acceptor and X is the transferred group. These are chemical species, so no SI unit applies.

On the MCAT: You are given a reaction or enzyme name and asked to classify it. Cues are names ending in -kinase or -transferase, or a group leaving one substrate and appearing on another without water being used. Typical examples are hexokinase in glycolysis, protein kinases in signaling, and transamination in amino acid metabolism.

Common confusion: A phosphatase is a hydrolase, not a transferase, because water accepts the phosphate. A ligase joins two molecules, usually using ATP, whereas a transferase moves a group between them. A mutase moves a group within one molecule, so it is an isomerase.