p103 and A60: novel proteins of the neuronal membrane-associated cytoskeleton.

Associated with the neuronal plasma membrane are cytoskeletal proteins which probably control the specialization of the membrane into axonal and dendritic domains. Specialized isoforms of the proteins spectrin and ankyrin are located in each region and provide molecular mechanisms for locating specific transmembrane proteins at required points. However, spectrin and ankyrin were defined by extensions of the model for the erythrocyte membrane, an analogy unlikely to provide a complete account of the neuronal membrane skeleton. We have defined two new proteins of the neuronal membrane skeleton, designated p103 and A60. p103 is enriched in post-synaptic densities and binds with high affinity to integral membrane proteins--we suggest that it may have a role in linking the cytoskeleton to synaptic glycoproteins. A60 is a 60 kDa axonal protein, which appears to form a lining to the axolemma. It is almost exclusively axonal, although some neurons (such as Purkinje cells) appear to contain it in the cell body and initial dendrite segment. A60 binds both ankyrin and neurofilaments, and may have a role in transmitting information critical to axonal morphology to the membrane.     

Methylation patterns at the hypervariable X-chromosome locus DXS255 (M27 beta): correlation with X-inactivation status.

Methylation patterns surrounding a hypervariable X-chromosome locus, DXS255, have been analyzed with the restriction enzyme MspI and its methylation-sensitive isoschizomer HpaII. HpaII sites flanking the hypervariable region were found to be methylated on 41 active X chromosomes and unmethylated on 11 inactive X chromosomes present in a range of male, female, and hybrid cells and tissues. This differential methylation pattern coupled with the previously described high level (greater than 90%) of heterozygosity at the DXS255 locus can therefore be applied to determine the inactivation status of X chromosomes in females heterozygous for X-linked disease and in tumor clonality studies.     

Lactate from cultures of Lactobacillus casei recovered in a fluidized bed column using ion exchange resin

Summary Lactic acid produced by continuous culture of L.casei in an upflow packed bed reactor, was recovered with Amberlite IRA 400 in a fluidized bed column. Bed expansions of 1.25 and 2.25 were applied. Reutilization did not alter the capability of net recovery of 0.048 ± 0.01 g lactic acid/g resin. When 2200 cm/h of ascensional velocity was used, (bed expansion of 2.25), the resin adsorbed 39.3% of the initial lactic acid and 63.5% was eluted. This resin supported the highest exchange capacity of 0.126 g lactic acid/g resin. Applying high flow rates, the process has potential industrial applications due to the short time employed.     

Na,K-ATPase extracellular surface probed with a monoclonal antibody that enhances ouabain binding.

The Na,K-stimulated ATPase is inhibited by extracellular cardiac glycosides, which bind to the enzyme's alpha subunit. We used a monoclonal antibody, VG4, as a probe of the extracellular surface. The antibody was specific for Na,K-ATPase and bound to intact cells. The epitope was mapped to the first extracellular loop (H1-H2) of alpha, using a combination of techniques including trypsinolysis, N-terminal sequence of a fragment containing the determinant, and analysis of the effects of species-specific sequence differences. The antibody inhibited Na,K-ATPase activity under certain circumstances, indicating that the H1-H2 loop participates in conformational changes that are transmitted to the active site. Mutations in the H1-H2 loop have been shown by others to affect ouabain affinity. Ouabain and the antibody acted synergistically to inhibit the enzyme, which seemingly supported the hypothesis that the H1-H2 loop is an essential part of the cardiac glycoside binding site. Direct measurements of the binding of [3H]ouabain, however, indicated that VG4 enhanced rather than inhibited binding, presumably by promoting favorable conformation changes. The data suggest the possibility that the cardiac glycoside binding site may be intramembrane rather than extracellular.     

Towards a biomolecular computer.

A new version of computing and information processing devices may result from major principles of information processing at molecular level. Non-discrete biomolecular computers based on these principles seems to be capable of solving problems of high computational complexity. One of the possible ways to implement these devices is based on biochemical non-linear dynamical systems. Means and ways to materialize biomolecular computers are discussed.