Tärkkelyssyntaasien

Tärkkelyssyntaasit, known in English as starch synthases, are enzymes crucial for the biosynthesis of starch in plants and some bacteria. These enzymes play a key role in converting glucose units into the complex polysaccharide starch. Starch serves as a primary energy storage molecule in plants, accumulating in specialized organelles called plastids, particularly amyloplasts and chloroplasts.

There are generally two main classes of starch synthases: soluble starch synthases (SSS) and bound starch synthases (often referred to as starch granule-bound synthases, GBSS). Soluble starch synthases are found in the stroma of plastids and are responsible for elongating existing glucan chains, primarily those of amylose, a linear component of starch. Bound starch synthases, on the other hand, are associated with the surface of the growing starch granule and are essential for the synthesis of amylopectin, the branched component of starch.

The process involves the transfer of glucose residues from adenosine diphosphate glucose (ADPG) to the non-reducing end of an existing glucan chain. This reaction is catalyzed by starch synthases, extending the polysaccharide chain by one glucose unit at a time. The coordinated action of various starch synthases, along with branching enzymes and debranching enzymes, ensures the precise formation of the characteristic branched structure of amylopectin and the linear chains of amylose, ultimately creating the starch granule. Mutations in genes encoding starch synthases can lead to altered starch structure, reduced starch content, or even starch-less phenotypes, highlighting their critical importance in plant metabolism and development.