PubMed Health⌕ Search

Biomedical subjects

A Yaron

Publications and source records attributed to A Yaron.

At least 37 records · Page 2Linked to original sources
PubMed1992

Angiotensin-I-converting enzyme and its correlation with human follicular fluid steroids.

Angiotensin-I-converting enzyme (ACE) is a peptidyl-dipeptide hydrolase which splits off the dipeptide His-Leu from the decapeptide angiotensin I and thus converts it to angiotensin II. We determined ACE activity in human preovulatory follicular fluid to further establish the intraovarian activity of the renin angiotensin system. Follicular fluids (n = 18) were obtained from eight patients undergoing in vitro fertilization (IVF) and embryo transfer (ET). ACE activity in follicular fluid and serum was determined by fluorescent spectrophotometry. The median follicular fluid ACE activity was 1.12 (range: 0.19-1.56) nmol/min/ml. This value was significantly lower than ACE activity in serum, 1.50 (range: 1.22-1.57) nmol/min/ml (P less than 0.001). In contrast to this 3:4 ratio between follicular fluid and serum ACE when expressed per ml fluid, the values were very similar when expressed per mg of protein: 0.025 vs. 0.023 nmol/min/mg in follicular fluid and serum, respectively. Correlations were sought between follicular fluid ACE activity and both serum and follicular fluid E2 and P4. A highly significant correlation (P less than 0.0005, r = 0.73) was found between ACE activity in follicular fluid and follicular fluid P4. The presence of significant ACE activity in human follicular fluid further supports the local-ovarian activity of the renin angiotensin cascade.

Embryo Transfer↗
PubMed1992

Distribution of proline-specific aminopeptidases in human tissues and body fluids.

The proline-specific peptidases, aminopeptidase P (EC 3.4.11.9) and dipeptidyl peptidase IV (EC 3.4.14.5), were measured in human tissue homogenates and physiological fluids. All tissues examined contained measurable aminopeptidase P and dipeptidyl peptidase IV activities. High specific activities for both enzymes under study were found in benign prostatic hypertrophy. Normal prostate and prostatic adenocarcinoma had a much lower activity. This difference, however, is not reflected in the serum values of the patients. The most striking finding is the extremely high activity of dipeptidyl peptidase IV in prostatosomes, prostate-derived organelles, which occur freely in human seminal plasma, and which are important for enhancement of sperm forward motility.

Adenocarcinoma↗
PubMed1992

Proline-specific aminopeptidases: potential role in bradykinin degradation.

The N-terminus of bradykinin is shown to be sequentially degraded by the human proline-specific aminopeptidases aminopeptidase P (EC 3.4.11.9) and dipeptidyl peptidase IV (EC 3.4.14.5). Additional evidence is provided for the hypothesis that these proline-specific aminopeptidases play an essential role in the degradation of peptides containing an N-terminal Xaa-Pro sequence.

Aminopeptidases↗
PubMed1991

Aminopeptidase P and dipeptidyl peptidase IV activity in human leukocytes and in stimulated lymphocytes.

Human white blood cells were shown to contain high aminopeptidase P activity. The specific activities found in the high-speed supernatant of the extracts of granulocytes, lymphocytes and monocytes ranged from 30 to 70 units per mg protein. Culturing lymphocytes during 7 days in the presence of phytohaemagglutinin resulted in a 70-200% increase in the specific aminopeptidase P activity and a 200% increase in the specific activity of dipeptidyl peptidase IV. The time-course of the activity of both aminopeptidase P and dipeptidyl peptidase IV during the stimulation of human T-lymphocytes by phytohaemagglutinin indicates an involvement of these two enzymes in the proliferative process of these immunocompetent cells. Due to their substrate specificity their potential substrates must have the N-terminal Xaa-Pro sequence known to be present in several immunologically important polypeptides.

Aminopeptidases↗
PubMed1991

Exopeptidases in human platelets: an indication for proteolytic modulation of biologically active peptides.

The determination in human platelets of four exopeptidases--aminopeptidase P, dipeptidyl peptidase IV, carboxypeptidase N, and angiotensin converting enzyme--by means of fluorometric or liquid chromatography techniques was carried out. The results obtained show that the specific activities of dipeptidyl peptidase IV, carboxypeptidase N, and angiotensin converting enzyme in intact and disrupted platelets are small compared to their specific activities in serum. However, for aminopeptidase P the specific activity of this enzyme is much higher in platelets than in serum. This suggests that circulating platelets may have a significant role as scavengers for circulating peptides containing bonds susceptible for aminopeptidase P.

Aminopeptidases↗
PubMed1990

Synthetic probes for the alpha-factor receptor.

The binding of the tridecapeptide yeast mating pheromone, alpha-factor, to its receptor represents an excellent model for the investigation of peptide hormone-receptor interactions. In this paper we present a number of strategies to probe the binding site of the alpha-factor receptor, and discuss the synthesis of probes containing radioactive and affinity tags. Preferential acylation of the alpha- or epsilon-amine in [Nle12]-alpha-factor was accomplished using 3-[3,5-diiodo-4-hydroxyphenyl] propanoic acid hydroxysuccinimide ester (diiodo Bolton-Hunter reagent). At pH 8.0 in a N-N-dimethylformamide/water mixture the ratio of epsilon- to alpha-acylation was 2.15 to 1, whereas at pH 6.5 in a 1,2-dimethoxyethane/water mixture alpha-acylation was favored by more than 3 to 1. The product distribution was found to depend on pH, organic cosolvent, and the ratio of organic solvent and aqueous buffer. Product distributions were followed using analytical high performance liquid chromatography and the products were characterized enzymatically and by mass spectrometry. Citraconic anhydride preferentially alpha-acylated [Nle12]-alpha-factor and served as a temporary masking group during the synthesis of epsilon-Bolton-Hunter acylated pheromone. Biotin or diiodo Bolton-Hunter reagents were also directly incorporated into [Nle12]-alpha-factor or Lys[Nle12]-alpha-factor during peptide synthesis. The peptides were assembled on a chloromethyl polystyrene resin or on a (phenylacetamido)methyl resin, and cleaved using anhydrous hydrogen fluoride (HF). Probes were inserted on amino groups either prior (biotin) or subsequent (Bolton-Hunter reagent) to HF cleavage. The biological activity of the synthetic peptides was characterized using growth arrest assays.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1988

Perinatal development of angiotensin-converting enzyme in the rat's blood.

Angiotensin-I-converting enzyme (ACE) activity was measured by a fluorimetric technique in serum samples taken from rat fetuses and their mothers. The samples were collected from anesthetized rats on consecutive days from day 18 of gestation to day 22 (day of delivery) and one day after birth. Fetal ACE activities were significantly higher than the corresponding maternal values which remained nearly unchanged during pregnancy. No dramatic changes in serum ACE activity of the developing fetuses could be observed.

Animals↗
PubMed1988

Angiotensin converting enzyme in bleomycin-treated patients.

Angiotensin converting enzyme activity (ACE) was measured in two patient groups treated with a bleomycin combination. One group, with squamous cell carcinoma was treated according to the Price et al. [1975] protocol, with low doses of bleomycin. The second group, with testicular tumors, was treated according to the Einhorn and Donohue [1977] protocol, with high doses of bleomycin. No change in serum angiotensin converting enzyme activity was observed in the low dosage group. A late and prolonged elevation, not connected to the acute injection, was observed in the high dosage group. There is an indication that the monitoring of ACE may be helpful in establishing the prognosis of the treated patients.

Bleomycin↗
PubMed1988

Assay of dipeptidyl peptidase IV in serum by fluorometry of 4-methoxy-2-naphthylamine.

A new fluorometric assay for determining dipeptidyl peptidase IV (DPP IV; EC 3.4.14.5) was developed. The synthetic substrate glycyl-L-proline-4-methoxy-2-naphthylamide (20 mmol/L), Tris buffer (50 mmol/L, pH 8.3), and serum (20 microL) are mixed and incubated. The reaction is stopped with citrate (100 mmol/L, pH 4.0) and the released 4-methoxy-2-naphthylamine is measured fluorometrically. The mean value of DPP IV activity in serum for 64 healthy subjects was 58 (SD 16) mumol of 4-methoxy-2-naphthylamine released per liter of serum per minute. The proposed procedure is sensitive, rapid, and accurate and can easily be automated.

2-Naphthylamine↗
PubMed1987

Aminopeptidase P activity in rat organs and human serum.

The substrate Lys(epsilon-Dnp)-Pro-Pro-NH-CH2-CH2-NH-ABz in which the fluorescent 2-aminobenzoyl (ABz) group (lambda ex = 320, lambda em = 410 nm) is intramolecularly quenched by the 2,4-dinitrophenyl (Dnp) chromophore was synthesized and used for the development of a sensitive assay for aminopeptidase P (EC 3.4.11.9). The emission of the intact compound was 160 times less than that of an equimolar concentration of Pro-Pro-NH-CH2-CH2-NH-ABz under the same conditions. The efficient resonance energy transfer permits an increased assay sensitivity as compared to the previously reported Phe(p-NO2)-Pro-Pro-NH-CH2-CH2-NH-ABz in which the p-nitrophenylalanyl [Phe(p-NO2)] residue caused only a 3.4-fold collisonal quenching. The kinetic constants Km were determined as 100 +/- 3.0 and 38 +/- 1.0 microM (mean of four experiments) for the human serum and the rat-lung enzymes, respectively. Both enzymes were inhibited by metal chelating agents and were not affected by 2.8 microM diisopropyl fluorophosphate. The mean activity in the sera of 53 healthy adults was 37.4 +/- 2.7 (standard error) with a standard deviation of 19.2 units/ml of serum. Only 10 microliters of serum was required for a reliable assay of the enzyme. The specific activity in rat-organ extracts was determined. High aminopeptidase P activity was observed in the testis, lung, kidney, and ovary and lower activity was observed in the serum.

Aminopeptidases↗
PubMed1984

Soluble and immobilized clostridial aminopeptidase and aminopeptidase P as metal-requiring enzymes.

The dependence of enzymatic activity on Co2+ concentration was found to be bell-shaped for the soluble and immobilized clostridial aminopeptidase (alpha-aminoacyl-peptide hydrolase, EC 3.4.11.13) and aminopeptidase P (aminoacylpropyl-peptide hydrolase, EC 3.4.11.9), with maxima in the 3-18 microM range of Co2+ concentration. The Co2+-enzyme association constants derived from the activation of soluble, glass- and cellulose-bound clostridial aminopeptidase by Co2+ were KE-Co = 5.2 X 10(5), 4.5 X 10(6) and 2.0 X 10(5) M-1, respectively; for soluble and glass-bound aminopeptidase P, the KE-Co were 1.5 X 10(5) and 8.2 X 10(5) M-1, respectively. Kinetic measurements indicate the involvement of Co2+ in the enzyme-substrate binding. Cobalt-citrate (Co-cit) acted as a useful metallobuffer and protected both enzymes against inhibition by high concentrations of CoSO4. For association of citrate with Co2+ under the assay conditions, KCo-cit was determined as (5.3 +/- 1.4) X 10(3) M-1 by anodic stripping polarography. In contrast to the rapid association of Co2+ with soluble and glass-bound clostridial aminopeptidase (less than 1 min at 4 degrees C), the dissociation process was very slow (hours to days), being slower for the glass-bound than for the soluble and cellulose-bound enzyme. For aminopeptidase P, both processes were rapid. All the interactions were shown to be reversible.

Aminopeptidases↗
PubMed1984

Renin, aldosterone, and serum-converting enzyme activity during normal and hypertensive pregnancy.

Plasma renin activity, plasma aldosterone, and serum-converting enzyme activity were measured in 13 normotensive pregnant women in three sequential periods: 19-21, 29-31, and 38-40 weeks of gestation. The converting enzyme activity was also measured in a group of 6 women with hypertensive pregnancy and an age-matched control group of 35 normal nonpregnant women. Plasma renin activity and plasma aldosterone values were both significantly elevated in the three periods of pregnancy, but plasma aldosterone levels were relatively lower during the first two periods. This is suggested to be secondary to depressed aldosterone secretion by intravascular volume expansion. The serum-converting enzyme activity did not change during pregnancy, and the mean values (1.02 +/- 0.27 U) were lower than those found in the control group (1.23 +/- 0.26 U). Similar low values were found in the hypertensive pregnancy group (1.11 +/- 0.35 U). Therefore, we assume that the converting enzyme is not a limiting factor in the conversion of angiotensin nor does it contribute significantly to the pathogenesis of hypertensive pregnancy.

Adult↗
PubMed1984

Serum angiotensin converting enzyme activity in normal adults and patients with different types of hypertension.

The serum converting enzyme activity (SCEA) was measured in 86 healthy individuals (1.44 +/- 0.82 u, mean +/- SD), 39 patients with essential hypertension (1.53 +/- 0.71 u), 7 patients with hypertension due to renal artery stenosis (1.76 +/- 0.77 u), 14 patients with chronic renal failure (2.10 +/- 0.57 u), 7 patients with renal failure and hypertension (2.62 +/- 0.35 u), 22 normotensive pregnant women (1.02 +/- 0.26 u) and 6 hypertensive pregnant women (1.1 +/- 0.3). No difference was detected between men and women or between normotensives and hypertensives. However, a significant rise in SCEA was found in patients with chromic renal failure (P less than 0.005), in whom an enlarged pulmonary vascular bed and accelerated cellular breakdown are thought to be the causes of the elevated SCEA. During pregnancy, subnormal SCEA was found (P less than 0.005), and this is thought to be due to the enzyme consumption in the kinin system, which is activated during pregnancy. We assume that converting enzyme is not a limiting factor in angiotensin conversion, and most probably it does not contribute significantly to the pathogenesis of hypertension.

Adult↗
PubMed1983

Sequential hydrolysis of proline-containing peptides with immobilized aminopeptidases.

Proline-containing polypeptides are shown to be sequentially degraded by two aminopeptidases. Clostridial aminopeptidase (EC 3.4.11-) cleaves off any N-terminal amino acid residue including proline from polypeptide chains, but does not cleave the N-terminal secondary peptide bonds involving a prolyl nitrogen. Aminopeptidase P (EC 3.4.11.9) cleaves exclusively such secondary bonds. The two enzymes were immobilized by coupling them covalently to porous amino glass beads. Highly stable preparations were obtained with unchanged pH optimum and thermal stability. The applicability of clostridial aminopeptidase to sequence determination was demonstrated by the time-dependent hydrolysis of enkephalin and Substance P octapeptide. Sequential hydrolysis with the two immobilized enzymes was demonstrated with the proline-containing (Pro-Gly-Pro)10, [Asn1, Val5]angiotensin II, bradykinin, Substance P and tuftsin. Absence of endopeptidase activities was demonstrated by resistance of cytochrome c to hydrolysis and by the ordered release of amino acids during the sequential degradation by immobilized clostridial aminopeptidase and aminopeptidase P.

Amino Acid Sequence↗