Inhibition of protein synthesis after intravenous or intramuscular challenge with diphtheria toxin

Inhibition of protein synthesis in guinea pig tissues after administration of diphtheria toxin varies significantly with the route of injection.

Specificity of leucine stimulation of insulin release

The ability of leucine to stimulate insulin release was studied in an in vitro system, using microdissected pancreatic islets with a high proportion of the insulin-producing <i>β</i>-cells. When tested in a glucose-free medium, L-leucine stimulated insulin release over a wide concentration range with maximum effect at about 20 mM. The stimulation of insulin release was additive to that elicited by 10 mM glucose. The L-configuration was essential for leucine to be recognized by the <i>β</i>-cells as an insulin secretagogue. L-isoleucine, alone or in combination with L-leucine, did not affect insulin release. It seems, therefore, unlikely that all sites for L-leucine transport are identical with receptor sites for stimulation of insulin release.

Protein synthesis in intestinal mucosa: the effect of route of administration of precursor amino acids

All cells in the intestinal villus of the rat are capable of synthesizing protein from amino acid precursors (l-leucine). Moreover, polyribosomes from both crypts and villi are equally able to incorporate l-leucine into protein. Unlike other tissues, e.g. liver, there is no diurnal variation of protein synthesis in the intestine of the unfed rat, whether leucine is administered intraluminally or intravenously. The route of administration of precursor (l-leucine) is important in determining which part of the villus incorporates the label into protein. After intravenous administration, protein from cells near the villus-crypt junction is most heavily labeled, whereas after intraluminal administration protein from cells near the villus tip is most heavily labeled. The pattern of proteins most heavily labeled by radioactive precursor is different in the villus when compared with proteins from the crypt cells. Smaller molecular weight membrane-bound proteins are preferentially labeled in the crypt cells, whereas on the villus the pattern of labeling is more evenly distributed among the various proteins. Moreover, intraluminal leucine is utilized for protein synthesis to a greater extent than that in the blood, when the concentration in both compartments is similar. Thus, intraluminal and intravenous injections of labeled precursor are not equivalent. Both routes should be considered in data for experiments measuring intestinal protein synthesis.

Electroshock effects on brain protein synthesis: relation to brain seizures and retrograde amnesia

The effects of electroshock on brain seizure activity and brain protein synthesis were studied in male mice. A significant but short-lasting inhibition of brain protein synthesis and an increase in the amount of free leucine were produced by electroshock at intensities above the brain seizure threshold. Electroshock at intensities below the brain seizure threshold did not affect brain protein synthesis.