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Biomedical subjects

F Stern

Publications and source records attributed to F Stern.

At least 37 records · Page 2Linked to original sources
PubMed1983

Cerebrocystatin suppresses degradation of myelin basic protein by purified brain cysteine proteinase.

Procedures are described for extraction or release, assay and purification of cerebrocystatin an inhibitor of brain cathepsin B or of papain. Neurosecretory regions of rat brain contained significantly higher amounts of cerebrocystatin compared to cortex, cerebellum, mid- and lower brain regions, and spinal cord. Inhibitor was purified to apparent homogeneity by alkaline treatment of rat brain cytosol, followed by gel-filtration and affinity chromatography on Reacti-gel coupled to alkylated papain. Purified cerebrocystatin was a single polypeptide of Mr 12,500 as shown by gel-electrophoresis on urea-SDS slab gels. Cerebrocystatin inhibited the hydrolysis of BANA by papain (Ki, 1 nM) or by purified rat brain cathepsin B (Ki, 10 nM) and suppressed the hydrolysis of myelin basic protein (MBP) by cathepsin B (I50, 0.8 microM) and prevented its cleavage to form polypeptides of Mr 15,000-17,000.

Animals↗
PubMed1983

Observations on N alpha-deacetylation of model amino acids and peptides: distribution and purification of a specific N-acyl amino acid releasing enzyme in rat brain.

N alpha-Acyl amino acid releasing enzyme (NAARE), an enzyme cleaving acetylMet-Ala at the Met-Ala bond was purified from rat brain cytosol to apparent homogeneity by salt precipitation, gel filtration, and several steps of ion exchange. Levels of NAARE exceeded acylase measured with acetylmethionine in all brain regions and subcellular fractions examined: 60% was associated with cytosol and the remainder with debris or the crude nuclear and mitochondrial-synaptosomal subfractions. Activity was highest in pituitary and was approximately 0.5-0.6 that of liver or kidney. The purified enzyme preferentially hydrolyzed acetylmethionyl peptides: Km for acetylMet-Ala was 0.93; Vmax, 3.5 nmol-1 (kcat, 1185) with pH optimum of 8.9 as compared with 8.2 for acylases measured in cytosol. The purified enzyme was devoid of acylase and common exo- and endopeptidase contamination. Structure-activity relationships examined with synthetic formylated or acetylated peptides indicated no significant effects for di- or tripeptides if the second substituent was Ala, Ser, Asn, or Thr, but the activity was reduced 0.5-fold for Leu, a branched-chain amino acid. No hydrolysis was observed for polypeptides with five or more residues having N-terminal acetylated Tyr (enkephalin) or Ser (alpha-melanocyte-stimulating hormone, thymosin alpha 1), supporting the notion that the enzyme plays a role only in turnover of smaller peptides formed perhaps as a result of endopeptidase cleavage of proteins or polypeptides containing acetylated Met at the N terminus.

Amidohydrolases↗
PubMed1981

Conversion of Met-enkephalin-Arg6-Phe7 by a purified brain carboxypeptidase (cathepsin A).

A carboxypeptidase A-like enzyme known as cathepsin A was purified from rat brain by extraction with Triton X-100, followed by chromatography on DEAE-Sephadex A-50 and gel-filtration. Purified enzyme was devoid of contamination of tryptic-like enzymes, by dipeptidyl carboxypeptidase (angiotensin converting enzyme) and of enkephalinnases cleaving the Tyr-Gly and Gly-Phe bonds of Met-enkephalin. Incubation of purified enzyme with Met-enkephalin-Arg6-Phe7, a naturally occurring enkephalin surrogate, was accompanied by the release of three products as detected by reverse phase HPLC. Subsequent amino acid analysis identified these as Phe, Met-enkephalin-Arg6, and Met-enkephalin, indicating cleavage at the Arg6-Phe7 and Met5-Phe6 bonds. Breakdown followed a precursor-product-relationship with the hexapeptide appearing as an intermediate and the pentapeptide as the final product. The Km for cleavage of the Arg-Phe site was 0.09 mM. Rates of cleavage of hexa- and heptapeptide accord with those found for synthetic N-protected dipeptide substrates. Cathepsin A does not act as an enkephalinase in the accepted sense, since no breakdown of Met-enkephalin was observed.

Amino Acid Sequence↗
PubMed1977

Lipoperoxidation in human and rat brain tissue: developmental and regional studies.

Lipoperoxidation in human and rat brain was studied on the basis of formation in vitro of thiobarbituric acid positive (TBA) materials. In rats aged 1--540 days, the endogenous pools of reactive material were unchanged but on subsequent incubation of their homogenates the level of TBA-positive materials fell by 3 fold (fresh weight basis) and 5.4 fold (protein basis). In human brain, there was a distinct regional distribution of reactive materials in the endogenous pools with highest levels in the cerebellar vermis, and lower levels in thalamus, cortical regions, substantia nigra, caudate nucleus, pallidum, putamen, and hypothalamus. Only trace levels were detected in the pineal gland. On incubation all values rose 13--25 fold within 3 h at 37 degrees C except for cerebellar vermis which was increased 6 fold, and pineal gland 9 fold. Four TBA-positive materials were separated from rat brain by TLC, three of which were identical to malonyldialdehyde and its polymers. Lipoperoxidation in rat homogenates was inhibited 75--90% by sera from several different sources. The inhibitory properties were unaffected by dialysis and were not reproduced by addition of a large number of low and high mol. wt. components including vitamin E when added in concentrations equal to or exceeding that of native serum.

Adult↗
PubMed1975

Changes in proteolytic enzymes and proteins during maturation of the brain.

(1) Changes during development in the levels of proteinases and peptidases were measured in brain homogenates. At all ages di- and tripeptidase levels were 7-15-fold higher than proteinase activity. (2) Cathepsin A and D and neutral proteinase activity first decreased (during the 5 days before birth) and then increased (primarily during the first 10 days after birth) in development. The total enzyme content per unit weight of brain did not change greatly after 10 days, although specific activity fell owing to an increase in protein in older animals. (3) The developmental pattern of activities or peptidases measured with Leu-Gly and Leu-Gly-Gly and of arylamidases measured with Arg- and Arg-Arg-beta-naphthylamides was similar to that of proteinases. Total and specific activities increased rapidly after birth; then total activity did not change and specific activity decreased. (4) The proteinase content of tissue fractions (nuclear and lysosomal-mitochondrial) similarly reached a maximal peak in the rapid growth phase of the brain. (5) The decrease of hydrolytic activity after 10 days of age seems to parallel a decrease in the rates of protein breakdown in vivo, showing parallel behavior with decreasing protein turnover. In contrast, during the first 10 days of life protein turnover and calculated rate of protein breakdown in vivo decrease while the level of hydrolytic enzymes increases.

Amino Acids↗