[a] & [b]: Isoenzyme (isozyme) is one of the several forms in which an enzyme may exist in various tissues, e.g. there are about 5 isozymes of enzyme lactic dehydrogenase. Although the isoenzymes are similar in catalytic qualities, they may be separated from each other by special chemical tests. Holoenzyme is a type of enzyme consisting of a protein portion (apoenzyme) and a non-amino acid part or prosthetic group.