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T N Akopyan

Publications and source records attributed to T N Akopyan.

9 recordsLinked to original sources
PubMed1994

Proteolytic processing of farnesylated peptides: assay and partial purification from pig brain membranes of an endopeptidase which has the characteristics of E.C. 3.4.24.15.

The proteolytic processing of farnesylated peptides was investigated with the tritiated C-terminal heptapeptide of mouse N-Ras protein, Propionyl-Gly-Ser-Pro-(farnesyl-Cys)-[3H]Val-Leu-Met, as substrate. Using two rapid and sensitive methods, the peptidase which cleaves the (farnesyl-Cys)-[3H]Val bond was purified more than 100 times from a microsomal fraction of pig brain. The determination of its molecular mass (about 70 kDa) and its pH range for optimum activity (neutral pH) as well as the results obtained with various inhibitors indicate that this [3H]Val-Leu-Met releasing enzyme resembles endopeptidase 24.15: a thiol-dependent zinc metallopeptidase. Parallel and comparative inhibition assays on partially purified enzyme and pure "24.15" confirm this similarity.

Amino Acid Sequence↗
PubMed1992

Cleavage of farnesylated COOH-terminal heptapeptide of mouse N-ras by brain microsomal membranes: evidence for a carboxypeptidase which specifically removes the COOH-terminal methionine.

Brain microsomal membranes are capable of sequentially removing Met, Leu and Val from a chemically synthesized COOH-terminal heptapeptide (propionyl-Gly-Ser-Pro-(farnesyl-Cys)-Val-Leu-Met) of mouse N-ras protein. The carboxypeptidase generating Met displays maximum activity at neutral pH and shows high affinity for the farnesylated substrate (Km = 73 microM) as compared to its non farnesylated precursor (Km = 600 microM). The results of inhibitor action suggest that the membrane carboxypeptidase is a novel, probably thiol-dependent, serine type peptidase.

Amino Acid Sequence↗
PubMed1988

Cystatins from bovine brain: purification, some properties, and action on substance P degrading activity.

Two cystatins were purified from tissue extract of bovine brain by alkaline treatment, acetone fractionation, gel chromatography on Sephadex G-75, and affinity chromatography on S-carboxymethyl-papain-Sepharose. One of the inhibitors had a relatively high molecular mass, 25 kDa (HMM-cystatin) with pI 4.7, and the other, 11 kDa (LMM-cystatin) with pI 5.23. Both inhibitors showed considerable stability at pH 2 and 80 degrees C. The cystatins inhibited papain, ficin, and cathepsins B and H, but not trypsin, chymotrypsin, thermolysin, nagarse, and cathepsin D. Ki values for the complexes of papain and the inhibitors were estimated to be 2.8 x 10(-10) M for HMM-cystatin and 1.3 x 10(-9) M for LMM-cystatin. Both purified cystatins prevented degradation of substance P by soluble fraction and lysosomal extract obtained from synaptosomes, but did not suppress the cleavage of the peptide by synaptosomal plasma membranes.

Animals↗
PubMed1985

Synaptosomal degradation of substance P and some other neuropeptides.

Synaptosomes purified from spinal cord and from different rat brain areas exhibit peptide hydrolase activity, cleaving substance P (SP), bradykinin, THRH, LHRH, and neurotensin. The lowest activity for all the peptides tested was found in spinal cord, while the region with the highest degrading activity depended on the substrate: for substance P, it was striatum and cortex; for bradykinin, hypothalamus, and medulla oblongata; for THRH, striatum; for LHRH, midbrain; and for neurotensin, hippocampus. Degradation of substance P takes place at the plasma membrane of synaptosomes. Synaptosome ghosts cleave substance P (pH optimum 7-9, Km-2.5 X 10(-5) M, Vmax-130 nmol . hr-1 . mg protein-1) and also a number of its C-terminal fragments. Effects of the inhibitors show that several different classes of peptidases and proteases are involved in the degradation process. Peptide cleavage represents the probable pathway of synaptosomal inactivation of substance P.

Animals↗
PubMed1979

Hypothalamic cathepsin D: assay and isoenzyme composition.

A sensitive and convenient method of endopeptidase assay using as substrate globin modified with pyridoxal-5-phosphate was used for determination of acid proteinases in bovine hypothalamus separated by isoelectric focusing. The soluble protein fraction of hypothalamus upon elution from Sephadex gave five peaks of proteinase activity at pH 3.2. The properties indicate that these peaks of endopeptidase activity are isoenzyme forms of cathepsin D.

Animals↗
PubMed1978

Acid proteinase of hypothalamus. Purification, some properties, and action on somatostatin and substance P.

In a continuing study of the physiological role of protein breakdown in the hypothalamus, acid proteinase from bovine hypothalamus was purified about 1000-fold. The molecular weight of the enzyme was approximately 50,000. Masimal activity against hemoglobin was obtained at pH 3.2-3.5; serum albumin was split much more slowly. Hypothalamus acid proteinase was partially inhibited by beta-phenyl pyruvate, or benzethonium Cl, and was completely inhibited by low concentrations of pepstatin. This proteinase splits somatostatin, substance P, and analogs of substance P. The probable sites of enzyme action on these peptides were determined by the end group dansyl technique. The enzyme, most likely cathepsin D, may play an important role in the formation and breakdown of peptide hormones in the hypothalamus.

Animals↗
PubMed1975

Beta-cyanoalanine synthase: purification and characterization.

Beta-cyano-L-alanine synthase [L-cysteine hydrogen-sulfide-lyase (adding HCN), EC 4.4.1.9] was purified about 4000-fold from blue lupine seedlings. The enzyme was homoegeneous on gel electrophoresis and free of contamination by other pyridoxal-P-dependent lyases. The enzyme has a molecular weight of 52,000 and contains 1 mole of pyridoxal-P per mole of protein; its isoelectric point is situated at pH 4.7. Its absorption spectrum has two maxima, at 280 and 410 nm. L-Cysteine is the natural primary (amino acid) substrate; beta-chloro- and beta-thiocyano can serve (with considerably lower affinity) instead of cyanide as cosubstrates for cyanoalanine synthase. The synthase is refractory to DL-cycloserine and D-penicillamine, potent inhibitors of many pyridoxal-P-dependent enzymes. Cyanoalanine synthase catalyzes slow isotopic alpha-H exchange in cysteine and in end-product amino acids; the rates of alpha-H exchange in nonreacted (excess) cysteine are markedly increased in the presence of an adequate cosubstrate; no exchange is observed of H atoms in beta-position.

Amino Acids↗