Biomedical subjects

A Azaryan

Publications and source records attributed to A Azaryan.

7 recordsLinked to original sources

PubMed1997

High-level expression of the prohormones proenkephalin, pro-neuropeptide Y, proopiomelanocortin, and beta-protachykinin for in vitro prohormone processing.

Prohormone substrates are required for investigation of the proteolytic processing of prohormones and proproteins into active peptide hormones and neurotransmitters. However, the lack of prohormone proteins has been a limiting factor in elucidating proteolytic mechanisms for conversion of prohormones into active peptides. Therefore, in this study, cloned cDNAs encoding the prohormones proenkephalin (PE), pro-neuropeptide Y (pro-NPY), pro-opiomelanocortin (POMC), and beta-protachykinin (beta-PT) were utilized to express recombinant prohormones in Escherichia coli. High-level expression of milligrams of prohormones was achieved with the pET3c expression vector utilizing the T7 promoter for production of PE, pro-NPY, and POMC, as demonstrated by SDS-PAGE gel electrophoresis, Western blots, and 35S-methionine labeling. In addition, beta-PT was expressed at high levels as fusion proteins with the maltose-binding protein and glutathione S-transferase by the pMAL-c and pGEX-2T expression vectors, respectively. Relative rates of processing by the established processing proteases "prohormone thiol protease" (PTP), 70-kDa aspartyl protease, and PC1/ 3 and PC2 (PC, prohormone convertase) were examined with purified PE, pro-NPY, and POMC. Distinct preferences of processing enzymes for different prohormones was demonstrated. PTP preferred PE and pro-NPY substrates, whereas little processing of POMC was detected. In contrast, the 70-kDa aspartyl protease cleaved POMC more readily than pro-NPY or PE. However, PC1/3 and PC2 prefer POMC as substrate. Demonstration of selectivity of processing enzymes for prohormone substrates illustrates the importance of expressing recombinant prohormones for in vitro processing studies.

Animals↗

PubMed1991

Stress-induced change in cerebral ATP+ubiquitin-dependent proteinase activity vary with age.

Stress-induced changes in cerebral ATP+ubiquitin-dependent proteinase activity were studied and the effect of age on it was checked. For that purpose 23,000 g supernatant prepared from whole brain of 3- and 7-month-old rats after 6h long immobilization stress were used. With azocasein as substrate, at pH 8.0 values of ATP+ubiquitin-dependent proteinase activity increased for 20% and 10% in 3- and 7-month-old animals respectively. Following 24 h long immobilization, values of cerebral ATP + ubiquitin-dependent activity in 3-month-old animals dropped by 16%. Data obtained indicate that immobilization stress affects ATP+ubiquitin-dependent proteinase activity and point to the contribution of age in the modulation of enzyme response to stress.

Aging↗

PubMed1989

The presence of ATP + ubiquitin-dependent proteinase and multicatalytic proteinase complex in bovine brain.

The presence of two distinct high-molecular-weight proteases with similar pH optima in the weakly alkaline region was shown in cytosol of the bovine brain cortex. They were separated by ammonium sulfate fractionation and each was further purified by DEAE-Sephacel, Sephacryl S-300, DEAE-Cibacron Blue 3GA-agarose, heparin-agarose, and Sepharose 6B chromatography. The larger enzyme (Mr 1,400 kDa), which precipitates at 0-38% ammonium sulfate saturation, seems to be active in ATP + ubiquitin (Ub)-dependent proteolysis; it has low basal caseinolytic activity that is stimulated 3-fold by ATP, and when Ub is present ATP causes a 4.5-fold stimulation. A second proteinase was also found to be present (Mr 700 kDa) that precipitates at 38-80% ammonium sulfate saturation, is composed of multiple subunits ranging in Mr from 18 to 30 kDa, and degrades both protein and peptide substrates, demonstrating trypsin-, chymotrypsin- and cucumisin-like activities. Catalytic, biochemical, and immunological characteristics of this proteinase indicate that it is a multicatalytic proteinase complex (MPC), whose enzyme activity, in contrast to that of MPC from bovine pituitaries (1-3), is stimulated 1.7-fold by addition of ATP in the absence of ubiquitin at the early steps of purification; this property is lost during the course of further purification. Both proteinases are present in the nerve cells, since the primary chicken embryonic telencephalon neuronal cell culture extracts contain both ATP + Ub-dependent proteinase and MPC activities.

Adenosine Triphosphate↗

PubMed1987

Human and bovine brain cathepsin L and cathepsin H: purification, physico-chemical properties, and specificity.

Cathespin L (EC 3.4.22.15) and cathepsin H (EC 3.4.22.16) have been purified from brain cortex to apparent homogeneity by a simultaneous procedure involving acid extraction of homogenate at pH 4.2, ammonium sulfate fractionation (30-80%), chromatography on pepstatin-Sepharose, CM-Sephadex C-50, DEAE-Sephadex A-50, phenyl- and concanavalin A-Sepharose and isoelectric focusing. Cathepsin L and cathepsin H were assayed in the presence of dithiothreitol and Na2EDTA (2 mM each) with Z-Phe-Arg-NHMec (pH 5.5) and Lys-NNa (pH 6.5) respectively. Cathepsin L consists of 2 polypeptide chains with Mr 25,000 and 5,000, Mr of cathepsin H is 28,000. Cathepsin L exists in brain tissue in two multiple forms with pI values 5.7 and 5.9, pI of cathepsin H is 6.8. Substrate specificity of these thiol proteinases was tested with proteins (pyridoxyl-hemoglobin, azocasein) and low Mr naphthylamide and methylcoumarylamide substrates: Lys-NNa, Arg-NNa, Dz-Arg-NNa, Z-Arg-Arg-NNaOMe, Z-Phe-Arg-NHMec, Z-Phe, Val-Arg-NHMec, Z-Gly-Gly-Arg-NHMec. Z-Phe-Arg-NHMec is the best substrate for cathepsin L (KM = 5 microM, Kcat = 21 s-1), Arg-NNa--for cathepsin H (KM = 0.1 mM, Kcat = 1.93 s-1), being endoaminopeptidase cathepsin H also hydrolyses Bz-Arg-NNa (KM = 0.7 mM, Kcat = 1.3 s-1). Both proteinases are inhibited by traditional inhibitors of cysteine proteinases and E-64, but leupeptin turned to be more effective inhibitor of cathepsin L (Ki = 2.4 nM) than of cathepsin H (Ki = 9.2 microM), the latter enzyme being sensitive to puromycin and benzethonium chloride as well.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1985

Action of brain cathepsin B, cathepsin D, and high-molecular-weight aspartic proteinase on angiotensins I and II.

The action of three previously isolated electrophoretically homogeneous brain proteinases--cathepsin B (EC 3.4.22.1), cathepsin D (EC 3.4.23.5), and high-molecular-weight aspartic proteinase (Mr = 90K; EC 3.4.23.-)--on human angiotensins I and II has been investigated. The products of enzymatic hydrolysis have been identified by thin-layer chromatography on Silufol plates using authentic standards and by N-terminal amino acid residue analysis using a dansyl chloride method. Cathepsin D and high-molecular-weight aspartic proteinase did not split angiotensin I or angiotensin II. Cathepsin B hydrolyzed angiotensin I via a dipeptidyl carboxypeptidase mechanism removing His-Leu to form angiotensin II, and it degraded angiotensin II as an endopeptidase at the Val3-Tyr4 bond. Cathepsin B did not split off His-Leu from Z-Phe-His-Leu. Brain cathepsin B may have a role in the generation and degradation of angiotensin II in physiological conditions.

Angiotensin I↗

PubMed1985

Some properties of human and bovine brain cathepsin B.

Cathepsin B has been purified 750-fold to apparent homogeneity from human and bovine brain cortex using ammonium sulfate fractionation (30-70%), chromatography on Sephadex G-100, CM-Sephadex C-50, and concanavalin A-Sepharose. Enzyme was assayed fluorometrically at pH 4.0 with pyridoxyl-hemoglobin in the presence of 1 mM DTT and 1 mM EDTA. Properties of the enzyme from the two sources proved to be similar. On disc PAGE the purified preparation produced two bands associated with proteinase activity that are due to existence of two multiple forms of brain cathepsin B with pI 6.1 and 6.8. The enzyme is completely inactivated by thiol-blocking reagents, leupeptin, E-64, and demands thiol compounds for its ultimate activity. Z-Phe-Ala-CHN2 is a potent inhibitor of the enzyme (K2nd = 1280 M-1S-1) in contrast to Z-Phe-Phe-CHN2 (K2nd = 264 M-1S-1). pH optimum in the reaction of hydrolysis of Pxy-Hb is 4.0-6.0, KM(app.) = 10(-5) M. Cathepsin B splits azocasein: pH optimum 5.0-6.0, KM(app.) = 2.2 X 10(-5) M, but inclusion of urea in the incubation medium depresses the azocaseinolytic activity of the enzyme 1.5-fold. It does not split Lys-NNap, Arg-NMec and is not inhibited by bestatin. The specific activity of brain cathepsin B with Z-Arg-Arg-NNapOMe at pH 6.0 is 10-fold higher than with Bz-Arg-NNap, Z-Gly-Gly-Arg-NNap is a poor substrate. With Z-Arg-Arg-NMec and Bz-Phe-Val-Arg-NMec the specific activity is 80 and 35%, respectively of that with Z-Phe-Arg-NMec.

Animals↗

PubMed1983

Cathepsin D from human brain: purification and multiple forms.

Cathepsin D was purified about 1000-fold from human brain cortex by a procedure involving ammonium sulfate fractionation (30-70%), Sephadex G-75 chromatography, affinity chromatography on pepstatin-Sepharose and isoelectric focusing. The enzyme was assayed fluorometrically at pH 3.2, the substrates used were globin or haemoglobin modified with pyridoxal-5'-phosphate. 6 multiple forms of cathepsin D were resolved in the isoelectric focusing step with pI values 4.4, 4.8, 5.3, 6.2, 6.5 and 6.8. Km of pyridoxal-globin and pyridoxal-haemoglobin for all 6 multiple forms is 1.8-2.0 X 10(-5) M and 1.3 to 4 X 10(-6) M, respectively, and Ki of pepstatin is 2-4 X 10(-9) M. Gel filtration of the multiple forms on Sephadex G-100 column showed that each has a molecular weight of about 50 000. Human brain cathepsin D has a pH optimum of 3.2 with a smaller second optimum at pH 4.0 (pyridoxal-haemoglobin being used as substrate). All the multiple forms have the same pH-dependence curve. On SDS-polyacrylamide gel electrophoresis the purified enzyme produced 3 bands approximately corresponding to Mr 50 000, 35 000 and 15 000. Study of the breakdown of substance P and its C-terminal heptapeptide by cathepsin D shows that cleavage occurs at the Phe-Phe linkages of both substrates tested.

Brain↗