Faculty Bibliography

The effect of alcohol on cerebral protein metabolism of mice was measured in experiments in which the specific activity of the administered labeled free amino acid was kept constant during the 2-h incorporation time. Alcohol inhibited brain protein synthesis, the degree depending on the dose administered, and an acute dose was more inhibitory than chronic administration. Part but not all of the inhibition was due to the hypothermia caused by alcohol. The degree of inhibition was similar in the 4 brain areas studied; in subcellular fractions, inhibition was greatest in the synaptosomal fraction. Maternal ingestion of alcohol resulted in inhibition of incorporation in brain of the fetus, but not of the suckling mouse. No inhibitory effect on protein breakdown could be established. It is likely that alcohol affects synthesis of various brain proteins to different degrees

Changes in the rates of degradation of Met- and Leu-enkephalin by brain aminopeptidase were measured by UV absorption after high-pressure liquid chromatography. The cleavage of enkephalin paralleled the generation of tyrosine. Captopril (SQ 14,225) stimulated enzyme activity, to a greater extent with Met- than with Leu-enkephalin. Pro-His-Pro-NH2, histidine, and histamine stimulated enkephalin aminopeptidase approximately twice as much as captopril. The sulfhydryl group of captopril was not the only factor in its effect. The addition of captopril did not change the pH optimum, and it stimulated enkephalin degradation between 25 and 50 degrees C

The supernatant fraction of centrifuged homogenate of brain tissue contains material that inhibits the saturable binding of [3H]cocaine to crude mouse brain membranes. This material was subjected to heat treatment to remove protein; further purification was achieved by filtering through an Amicon UM-10 membrane ultrafilter and gel filtration of the ultrafiltrate on Sephadex G-25. Sensitivity to acid hydrolysis and peptidase action indicates that the inhibitory activity resides in peptide material with low molecular weight. The partially purified inhibitor has similar effects to that of cocaine on the specific binding of various ligands to opiate and nonopiate receptors in mouse brain membranes

The properties of the uptake of nucleosides and nucleotides by brain cells were examined in slices of mouse brain. Of the compounds tested, adenine and adenosine had the most rapid uptake and reached the highest levels. Uptake was mediated, as shown by saturability and strong inhibition, by low temperature, or by cyanide, and was only partially sodium- or calcium-dependent. The inhibition pattern by analogues indicated the presence of several uptake systems (possibly four), as shown by differences between adenine and guanine uptake, between adenine and adenosine uptake, and between adenosine and cytidine uptake. The properties of uptake systems for nucleotides and nucleosides were somewhat different from those for amino acids

Prolylleucylglycinamide (MIF) at 1.0 mM concentration and pH 7.0 was hydrolyzed by mouse brain homogenate at a rate of 140 nmol/mg protein/hr. Nearly all of this activity can be accounted for by the action of two enzymes, both of which cleave Pro and Leu sequentially from the N-terminus of MIF. At pH 7.0 the predominant enzyme is arylamidase, inhibited by puromycin (1 mM) and Mn2+ (2.5 mM). At pH 8.5, in the presence of Mn2+, a second enzyme with a higher potential activity (570 nmol/mg protein/hr) was observed. While the arylamidase is primarily localized in the cytosol, the Mn2+-stimulated enzyme is equally divided between soluble and particulate fractions. Because of its ability to cleave leucinamide, its high pH optimum, and its Mn2+ dependence, it can be classified as a leucine aminopeptidase (LAP). In its substrate specifically and its preference for Mn2+ over Mg2+ it resembles the LAP from connective tissue more than that from other sources

Purified of prolidase from calf brain (acetone and [NH4]2SO4 fractionation) separated this enzyme from proteases, leucine aminopeptidase, master dipeptidase, and Gly-Gly dipeptidase. Prolidase was tested with peptidase and protease inhibitors, used at higher levels (35 times or more) than their ID50 for peptidases and proteases. Bacitracin, leupeptin, chymostatin, and antipain had no effect; pepstatin slightly increased activity, and only bestatin was inhibitory. Antibiotics that affect protein synthesis did not inhibit prolidase. Peptides with proline at the NH2 end activated prolidase, whereas those with proline at the carboxyl end inhibited it. Di, tri, and tetra-Pro peptides increased prolidase activity. Thyrotropin-releasing hormone had no effect on prolidase; its analog Pro-His-Pro-NH2 gave high activation and decreased the Km from 20 mM to 1.54 mM. Pro-peptide inhibitors and activators were not themselves split by prolidase. The results indicate influences of specific peptides, for both inhibition and activation, on prolidase activity