METHIONINE ADENOSYLTRANSFERASE - STRUCTURE AND FUNCTION

Methionine adenosyltransferase (MAT), a key enzyme in metabolism, cata lyzes the synthesis of one of the most important and pivotal biologica l molecules, S-adenosylmethionine. In every organism studied thus far, MAT exists in multiple forms; most are encoded by related, but distin ct genes. Molecular and immunological studies revealed the presence of considerable conservation in the structure of MAT from different spec ies; however, the various MAT isozymes differ in their physical and ki netic properties in ways that allow them to be regulated differently. Recent studies suggest that human MAT is composed of nonidentical subu nits that can assume multiple states of aggregation, each with differe nt kinetic characteristics. The tissue distribution of MAT isozymes an d the ability of cells within the same tissue to switch between the di fferent forms of MAT suggest that this mode of regulation is important for cellular function and differentiation. Therefore, understanding t he regulation and structure-function relationship of this fascinating enzyme should help us clarify its role in biology and may provide us w ith tools to effectively manipulate its activity in clinical situation s such as cancer, autoimmunity and organ transplantation.