Analysis of Tissue Specific Expression Patterns of Isozymes

Isozymes are enzymes catalyzing the same biochemical reaction, but differ in amino acid sequences. They usually display different kinetic parameters, or express different regulatory properties. In addition some isozymes show tissue-specific expressions. These differences are considered that isozymes have properties related to the tissue-specific environments. Aldolase, one example of isozymes, has three isozymes A, B and C, and those isozymes are produced from different genes respectively. Aldolase A is usually produced at greater amounts in adult muscle. In adult liver, while aldolase A expression is repressed, aldolase B is produced. On the other hand, aldolase C mainly works in brain. These three isozymes also show different reactivity against substrates. While some isozyme groups are well studied, there have been no reports of comprehensive analyses of isozymes. Furthermore, isozymes are not distinguished in many publicly available genome databases. This is probably because there is no clear criteria to identify isozymes. In this report, we analyzed tissue-specific gene expressions of human enzyme genes and those paralogs, and searched tissue-specific pathways, to find an apparent criterion to distinguish isozymes and to detect new isozymes.