[Concept of isoenzymes in clinical points of views]

In the fields of clinical medicine, the word "isoenzyme/isozyme" was widely and easily used for the heterogeneities of plasma enzymes. The word "isozyme" seemed to be synonym for the multiple forms of enzymes. The Committee of Biochemical Nomenclature in IUPAC/IUB proposed six categories for multiple forms of enzymes in 1776. In this paper, additional four categories were proposed for the understanding the clinical significance of enzyme heterogeneities. These categories were follows, 1) enzyme linked immunoglobulins. 2) protease modified heterogeneities of plasma enzymes. 3) membrane associated plasma enzymes. 4) different enzymes reacted for the same substrates. Including these four classes, "isozyme", the multiple forms of enzymes in clinical uses were clearly categorized for clinical purposes.