Activation of receptors for a wide variety of hormones and neurotransmitters leads to an increase in the intracellular level of calcium. Much of this calcium is released from intracellular stores but the link between surface receptors and this internal calcium reservoir is unknown. Hydrolysis of the phosphoinositides, which is another characteristic feature of these receptors, has been implicated in calcium mobilization. The primary lipid substrates for the receptor mechanism seem to be two polyphosphoinositides, phosphatidylinositol 4-phosphate (PtdIns4P) and phosphatidylinositol 4,5-bisphosphate (PtdIns4,5P2), which are rapidly hydrolysed following receptor activation in various cells and tissues. The action of phospholipase C on these polyphosphoinositides results in the rapid formation of the water-soluble products inositol 1,4-bisphosphate (Ins1,4P2) and inositol 1,4,5-trisphosphate (Ins1,4,5P3). In the insect salivary gland, where changes in Ins1,4P2 and Ins1,4,5P2 have been studied at early time periods, increases in these inositol phosphates are sufficiently rapid to suggest that they might mobilize internal calcium. We report here that micromolar concentrations of Ins1,4,5P3 release Ca2+ from a nonmitochondrial intracellular Ca2+ store in pancreatic acinar cells. Our results strongly suggest that this is the same Ca2+ store that is released by acetylcholine.

Release of Ca2+ from a nonmitochondrial intracellular store in pancreatic acinar cells by inositol-1,4,5-trisphosphate.

Inositol phospholipids and cell surface receptor function.

Identification of 23 complementation groups required for post-translational events in the yeast secretory pathway

Various extracellular informational signals such as those from a group of hormones and some neurotransmitters appear to be passed from the cell surface into the cell interior by two routes, protein kinase C activation and Ca2+ mobilization. Both routes usually become available as the result of an interaction of a single ligand and a receptor and act synergistically to evoke subsequent cellular responses such as release reactions. The signal-dependent breakdown of inositol phospholipids, particularly phosphatidylinositol bisphosphate, now appears to be a key event for initiating these processes.

https://science.sciencemag.org/content/sci/225/4668/1365.full.pdf

Turnover of inositol phospholipids and signal transduction

Foreign gene expression in yeast: a review.

Controlled acetolysis of yeast mannans yields mixtures of oligosaccharides with (1→2) and (1→3) linkages between the mannose units, whereas the less stable (1→6) linkages of the polysaccharide backbone are cleaved. The “fingerprints,” obtained by gel filtration of the oligosaccharide mixtures, can be used to distinguish between the different yeast mannans. The general method may be useful for determining the taxonomy of yeasts and for making correlations between immunochemical reactivity and mannan structure.

Method for Fingerprinting Yeast Cell Wall Mannans

Publisher Summary The chapter focuses on the new developments concerning yeast mannan structure and biosynthesis as they relate to the organization of the cell wall and the roles played by these glycoproteins. The mechanism of mannan biosynthesis is still in a rudimentary state, partly because of the insufficient knowledge concerning mannan structure and partly because of the inherent difficulties in working with such a complex macromolecule. Detailed information of Saccharomyces cerevisiae mannan can now be sketched and facilitates the planning of experiments on, and the interpretation of results from, biosynthetic studies. Moreover, the availability of mannan mutants with known polysaccharide structural alterations should prove advantageous. Studies of mannan biosynthesis have taken three general tacks. One approach has been directed toward an elucidation of the overall process of mannan formation and translocation within the cell using “pulsechase” techniques and autoradiography. The second approach has dealt with the formation and secretion of intact mannan molecules by yeast protoplasts and the inhibition of this process by compounds that prevent protein or polysaccharide synthesis. The third approach has investigations of the enzymic processes involved in mannan synthesis, using cell-free extracts and following incorporation of radioactive mannose into endogenous and exogenous acceptors. The chapter discusses the detailed structures of specific yeast mannans.

Clinton E. Ballou

Papers

Method for Fingerprinting Yeast Cell Wall Mannans

Structure and Biosynthesis of the Mannan Component of the Yeast Cell Envelope

Isolation, characterization, and properties of Saccharomyces cerevisiae mnn mutants with nonconditional protein glycosylation defects.

Characterization of the Carbohydrate Fragments Obtained from Saccharomyces cerevisiae Mannan by Alkaline Degradation

Studies on the enzyme enolase. I. Equilibrium studies.