Evidence for a neutral proteinase in brain tissue

Separation of acid and neutral proteinases of brain

1. Cerebral proteinases were separated on Sephadex G-100 columns into acid and neutral fractions free from cross-contamination. Acid proteinases were more stable and were purified by additional steps with salt and pH5.0 precipitations, column chromatography on DEAE- or CM-cellulose and free-flow electrophoresis. 2. The separation made it possible to study the properties of the partially purified enzyme fractions. Some of these properties, such as K(m) with selected protein substrates, pH optima and temperature-dependence in the presence and absence of substrates, are described. 3. No requirement for metal ions or added cofactors was demonstrated. Neutral-proteinase activity was more sensitive to inhibition by heavy-metal ions; its activity could be increased by thioglycollate and glutathione, and inhibited by thiol reagents. Neutral and acid proteinases were inhibited by the chymotrypsin inhibitor chloromethyl l-2-phenyl-1-toluene-p-sulphonamidoethyl ketone. 4. In the presence of the appropriate synthetic substrates no cathepsin A activity was found, and only trace quantities of cathepsin B or C activities, which were more than 50-fold less than cathepsin D-like activity.

ENTRY OF GLUCOSE CARBON INTO AMINO ACIDS OF RAT BRAIN AND LIVER IN VIVO AFTER INJECTION OF UNIFORMLY 14-C-LABELLED GLUCOSE

1. Measurements were made of the rate of incorporation of (14)C from uniformly (14)C-labelled glucose into individual amino acids of rat brain and liver. 2. At 2.5 min. after intravenous injection of uniformly (14)C-labelled glucose, about 30% of the total radioactivity in the brain was present in the five amino acids studied. At 30 min. after subcutaneous injection the distribution of (14)C in amino acids was: in brain, alanine 2%, gamma-aminobutyrate 4%, aspartate 9%, glutamine 9% and glutamate 37% (total 69%); in liver, alanine 3%, aspartate 2.6%, glutamine 5.3% and glutamate 5.2% (total 18%). About 1% of the total radioactivity was in serine and glycine. 3. In both organs the specific radioactivity of alanine was initially higher than that of the other amino acids examined. The specific radioactivity of gamma-aminobutyrate in the brain was about the same as or higher than that of glutamate. 4. Amino acids of the rat brain were separated into ;free' and ;bound' fractions from brain dispersions in saline (or sucrose) media. Definite differences in the specific activities of the ;bound' and ;free' forms were not apparent.

Cleavage of myelin basic protein by neutral protease activity of human white matter and myelin

Polypeptides arising from neutral in vitro proteolysis of myelin basic protein (MBP) of human brain were evaluated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. At pH 7 a marked breakdown of MBP resulted in the formation of 8-12 polypeptides ranging from 6 to 17 kd in molecular weight. As neutral proteolytic activity was not eliminated by either gel filtration or cation-exchange chromatography acid-soluble protease(s) involved probably have a size and electric charge similar to that of MBP. The enzymatic nature of neutral proteolysis was ascertained by heat inactivation and inhibition by alpha 2-macroglobulin. Incomplete inhibition of proteolysis and the failure of small peptides (less than 6 kd) to show up on electrophoresis seem to suggest that MBP was degraded by exopeptic proteases as well. Acid extracts of purified myelin yielded polypeptides similar to those of MBP of delipidated white matter. The results are consistent with a sequential limited proteolysis of MBP by neutral proteases probably associated with myelin and possibly related to the in situ catabolism of MBP in man.

Proteases of human brain

Growing appreciation of the multiple functions of proteolytic enzymes in intracellular protein degradation and post-translational modification, in the release of biologically active macromolecules and peptides from precursors and in cellular protein regulation and quality control has stimulated interest in proteases in neurobiology and neuropathology. In this article, the proteinases and peptidases thus far studied in the human central nervous system are reviewed with respect to their enzymology, anatomical and cytological distributions and contributions to neurological and psychiatric disease states. Though information concerning brain proteases in man is fragmentary, it suffices to establish the importance of these complex systems for advancing knowledge of human cerebral function in health and disease.

Proteolytic activity at neutral pH in bovine spleen

Proteolytic activity at neutral pH can be demonstrated in extracts from beef spleen. This activity is completely due to an aminopeptidase - or a number of aminopeptides - which is able to hydrolyse proteins completely to amino acids. No evidence was found for the presence of endopeptidases active at neutral pH. The enzyme resembles to some extent swine kidney aminopeptides.