Highly conserved Methionine Adenosyltransferase (MAT) isoenzymes

It has been shown that changes of intracellular levels of S-adenosylmethionine (SAM) are related to the well beings of cells and organisms. The fluctuation of SAM level is cause by imbalance between SAM synthesis and metabolic pathways (methylation, transsulfuration and aminiopropylation) or degradation. S-adenosylmethionine biosynthesis is strictly and solely dependent on the activity of Methionine Adenosyltransferase (MAT, E.C.2.5.1.6), also known as S-adenosylmethionine synthetase. The methionine adenosyltransferase is encoded by two genes, MAT1A and MAT2A, encode for two homologous MAT catalytic subunits, α1 and α2. MAT1A is expressed in normal liver, and it encodes the α1 subunit found in two native MAT isozymes, which are either a dimer (MAT III) or tetramer (MAT I) of this single subunit. MAT2A encodes for a catalytic subunit (α2) found in a native MAT isozyme (MAT II), which is associated with a regulatory subunit (β) in encoded by MATA2B gene. MAT1A is expressed mostly in the adult normal hepatocytes, whereas MAT2A is widely distributed, of which mainly investigated are among highly proliferating liver cells, such as fetal liver and liver cancer cells. Except for parasites that rely on host for living, cells from all organisms have methionine adenyltransferase. MAT genes have been found to be exceptionally conserved throughout evolution.