The enzymes which catalyze the same reaction but have different amino acid compositions are commonly referred as :

The correct answer is A, Isoenzymes. Isoenzymes, also called isozymes, are different molecular forms of an enzyme that speed up the same chemical reaction but differ in their amino acid sequence. Because their structure differs, they can have different properties such as optimum pH, affinity for the substrate and the tissue in which they are found. The classic example is lactate dehydrogenase, which exists in five isoenzyme forms in the human body; the heart form and the liver form differ, and doctors measure them to detect damage to a particular organ. Creatine kinase isoenzymes are similarly used to diagnose a heart attack. Option B is wrong because isotopes are atoms of the same element with different numbers of neutrons, such as carbon-12 and carbon-14. Option C is wrong because isomers are chemical compounds with the same molecular formula but different structures, like butane and isobutane. Option D is wrong because coenzymes are small non-protein organic molecules, often made from vitamins, such as NAD, that help an enzyme work. Exam tip: isoenzymes: same reaction, different protein; LDH has five forms.