3.3 Each enzyme is given a systematic name which identifies the reaction catalyzed(e.g, hexokinase is named as ATP glucose phosphotransferase). 3.4 Each enzyme is assigned a four-digit number with the first digit denoting the class it belongs, the other three further clarifications on the reaction catalyzed3.3 Each enzyme is given a systematic name which identifies the reaction catalyzed (e.g., hexokinase is named as ATP:glucose phosphotrasferase). 3.4 Each enzyme is assigned a four-digit number with the first digit denoting the class it belongs, the other three further clarifications on the reaction catalyzed