Biosynthesis of glycosaminoglycans in foraminifera: A review

Organic matrix deposits in the tests of benthic and planktic foraminifera contain glycosaminoglycans as a major component. They are present in organic linings, organic cements and secretion products. Following cytological, autoradiographic, and molecular cell biological studies in plants and animals, the intracellular process for glycosaminoglycan production is choreographed by ribosomes, the endoplasmatic reticulum and the Golgi complex. Synthesized proteins released from the ribosomes on the granular endoplasmic reticulum are glycosylated and sulfated in a multistage process within the Golgi compartments. The completed glycosylated proteins are shed as vesicles (secretory vesicles?) into the cytoplasm. Along microtubular strands the vesicles are transported to the cell membrane and either formed into organic linings or organic cements or are secreted. As indicated by their composition both the secretion of organic material by foraminifera as well as the production of organic linings and organic cements are caused by the same intracellular mechanism. Some aspects of the relation between macromolecular preorganization of the glycosaminoglycan-rich template and patterns of biomineralization are discussed.