Okadaic acid: a new probe for the study of cellular regulation

The tumour promoter okadaic acid is a potent and specific inhibitor of protein phosphatases 1 and 2A. Here we review recent studies which demonstrate that this toxin is extremely useful for identifying biological processes that are controlled through the reversible phosphorylation of proteins.     

Isolation and structural analysis of a peptide containing the novel tyrosyl-glucose linkage in glycogenin.

The glucosylation site on glycogenin, the protein primer required for de novo glycogen synthesis, has been identified. The glucose is attached at position C1 in a glycosidic linkage with a unique tyrosine, and the sequence surrounding this residue was found to be: His-Leu-Pro-Phe-Ile-Tyr-Asn-Leu-Ser-Ser-Ile-Ser-Ile-Tyr(Glc)-Ser-Tyr-Leu -Pro- Ala-Phe-Lys. The same tyrosine residue is glycosylated whether glycogenin is isolated as a complex with the catalytic subunit of glycogen synthase, or covalently attached to glycogen. The possibility that insulin and growth factors may enhance glycogen synthesis via stimulation of the priming reaction is discussed.     

Three-dimensional structure of the regular surface glycoprotein layer of Halobacterium volcanii from the Dead Sea

A three-dimensional reconstruction from electron micrographs of negatively stained cell envelopes of Halobacterium volcanii has revealed the structure of the surface glycoprotein to a resolution of 2 nm. The glycoprotein is arranged on a p6 lattice with a lattice constant of 16.8 nm. It forms 4.5 nm high, dome-shaped, morphological complexes with a narrow pore at the apex opening into a `funnel' towards the cell membrane. The polarity of the structure was derived from freeze-etching experiments and `edge' views. Six radial protrusions emanate from each morphological complex and join around the 3-fold axis to provide lateral connectivity. Using the primary structure of the surface glycoprotein of the closely related species Halobacterium halobium (Lechner and Sumper, 1987) and the cell envelope profile from a previous X-ray analysis of the same species (Blaurock et al., 1976) we have integrated our reconstruction into a model of halobacterial cell envelope.     

Schistosoma mansoni: characterization of clones maintained by the microsurgical transplantation of sporocysts

Five male and 5 female clones of Schistosoma mansoni were established and maintained for 3 yr by the serial microsurgical transplantation of sporocysts from infected to uninfected Biomphalaria glabrata snails. The clones were initially derived from 10 randomly selected snails with monomiracidial infections. Clones were characterized by several criteria, including their infectivities for mice and snails, their cercarial outputs, and their ability to produce immunity in mice. The mean infectivities of individual clones in mice ranged from 26 to 44%, and were highly consistent within each clone. The infectivities of cloned sporocysts in snails ranged from 44 to 100% and were also highly consistent within clones. Mean cercarial outputs from individual clones ranged from 450 to 4,300 per snail. In mice, clones differed significantly from each other in their ability to immunize and in their susceptibility to immunity. Each clone was unique and did not appear to differ with time or subpassaging through snails, suggesting that the differences had a genetic basis.     

Depletion of Brain Glutathione in Preweanling Mice by L-Buthionine Sulfoximine

Previous studies indicated that DL-buthionine sulfoximine (DL-BSO), an agent that inhibits the biosynthesis of GSH in liver and other peripheral organs, fails to suppress levels of GSH in the CNS. In the current study, preweanling mice responded to repeated injections of L-BSO with marked declines (79.6-86.5%) of GSH content in brain and spinal cord. In adult mice, the same treatment schedule produced only modest declines (17.8-29.2%) of GSH content in brain and a 55.9% decline in spinal cord. Pretreatment of preweanling mice with L-BSO represents a tool for studying the role of GSH in the CNS.