Pääisoentsyymiä

Pääisoentsyymiä refers to a key or primary isoenzyme within a family of enzymes that catalyze the same biochemical reaction but have different molecular structures. Isoenzymes, also known as isozymes, are variants of enzymes that differ in amino acid sequence but not in catalytic activity. These differences can arise from genetic variations, alternative splicing of mRNA, or post-translational modifications.

The concept of a "pääisoentsyymiä" highlights the fact that within a group of isoenzymes, one may be considered the most significant or predominant due to its higher expression levels, greater catalytic efficiency under physiological conditions, or a more crucial role in a particular metabolic pathway. Identifying the pääisoentsyymiä is important in biochemical research and diagnostics as it can help understand normal physiological processes and how their dysregulation might contribute to disease.

For example, in lactate dehydrogenase (LDH), there are five different isoenzymes (LDH-1 to LDH-5). Each isoenzyme is a tetramer composed of different combinations of two subunit types, H (heart) and M (muscle). While all LDH isoenzymes catalyze the interconversion of lactate and pyruvate, their relative abundance varies in different tissues and can change in response to various conditions, such as myocardial infarction or liver disease. In such cases, one specific isoenzyme might be considered the "pääisoentsyymiä" in a particular tissue or under certain pathological circumstances, offering valuable diagnostic information.