Rapid fractionation of cell suspensions with the use of brominated hydrocarbons

Isolated hepatocytes can be rapidly separated from the suspending medium using an inexpensive, easily constructed centrifuge tube and a water immiscible liquid which has a density high enough to preclude the medium but low enough to permit sedimentation of cells. For that purpose, mixtures of either bromododecane or bromodecane with dodecane work well and have viscosities that are 30 to 50 times lower than that for the widely used silicon oils. As tests of the method, ATP, urea, and chloride were determined in suspensions and in cell and medium fractions. All of the ATP in cell suspensions was recovered in the cell fraction while most of the urea was in the medium. Chloride was about 10 mm in fresh hepatocytes, but, after 10 min at 38°C, the intracellular level of this ion returned to that found for the liver in vivo, 40–50 mm.     

Re-activation by glutamate or aspartate of amino-oxyacetate-inhibited aspartate aminotransferase in vitro and in isolated hepatocytes

Experiments with isolated rat hepatocytes and with cell extracts indicate, in contrast with previous reports, that pyruvate does not block or reverse the inhibition of aspartate aminotransferase (EC 2.6.1.1) by amino-oxyacetate. That inhibition, however, is partially overcome by glutamate or aspartate either in cell extracts or in whole cells incubated with substrate combinations that cause accumulation of those amino acids.     

On the origins of esterases

Comparisons among the primary sequences of five cloned eukaryotic esterases reveal two distinct lineages, neither bearing any significant overall sequence similarity to the functionally related serine protease multigene family. We have not eliminated the possibility that the esterases may have residual conformational similarities to the serine proteases. However, our profile analysis and analyses of the predicted conformations of the esterases reveal little similarity to the serine proteases. Four of the esterase proteins share 27%-53% overall sequence similarity and evidence of a catalytic mechanism involving the same Arg- Asp-Ser or His-Asp-Ser charge relay. We propose that these four esterases, three of them cholinesterases, form part of a multigene family essentially separate from the serine proteases.      

Effect of acyl chain length on the structure and motion of gramicidin A in lipid bilayers

The transmembrane ion transport properties of gramicidin A have previously been shown to dependent on the nature of its lipid environment. Solid-state NMR spectroscopic studies of 13C-labelled analogues of gramicidin in oriented multilayers of phosphatidylcholine have shown that variation of the lipid hydrocarbon chain length has no effect on the structure or orientation of the peptide backbone.