Effects of gas composition and pH on kinetics of lung angiotensin-converting enzyme

1987 ◽  
Vol 62 (3) ◽  
pp. 1216-1221 ◽  
Author(s):  
D. A. Rickaby ◽  
R. D. Bongard ◽  
M. J. Tristani ◽  
J. H. Linehan ◽  
C. A. Dawson
Keyword(s):  
Angiotensin Converting Enzyme ◽  
Surface Area ◽  
Ph Dependence ◽  
Gas Composition ◽  
Converting Enzyme ◽  
Hydrolysis Process ◽  
Hypoxic Vasoconstriction ◽  
Ace Activity ◽  
Kinetics Of ◽  
Hydrolysis Of

Given the pH dependence of enzymes in general and the potential importance of a blood and alveolar gas composition dependency on the interpretation of changes in the hydrolysis of angiotensin-converting enzyme (ACE) substrates by pulmonary endothelial ACE, we examined the influence of Pco2 and Po2 on the hydrolysis of a synthetic ACE substrate (benzoyl-phenylalanyl-alanyl-proline, BPAP) on passage through isolated rabbit lungs. Perfusate pH values of about 7.1, 7.4, and 7.9 were obtained by ventilating the lungs with gas containing different CO2 concentrations and Po2 values of approximately 110 and approximately 10 Torr were obtained by varying the concentration of O2 in the ventilating gas mixture. In the range studied neither acidosis nor alkalosis produced any significant changes in BPAP hydrolysis or in the kinetic parameters, Vmax and Km, for the hydrolysis process. On the other hand, a reduction in BPAP hydrolysis was detected when the Po2 was reduced from 110 to 10 Torr. The Vmax for BPAP hydrolysis by the lung was inversely correlated with the magnitude of the hypoxic vasoconstriction that occurred, suggesting that the reduced BPAP hydrolysis with hypoxia was due to the loss of perfused surface area due to the vasoconstriction. The results suggest that correlations between Pco2 and/or pH and whole-lung ACE activity that might occur in diseased lungs do not imply causalty. The hemodynamic consequences of changing Po2 (i.e., hypoxic vasoconstriction) may alter whole-organ ACE activity in the sense of changing the perfused surface area (i.e., the amount of ACE in contact with flowing perfusate).

Angiotensin converting enzyme in brush-border membranes of avian small intestine

1988 ◽  
Vol 135 (1) ◽  
pp. 1-8
Author(s):  
B. R. Stevens ◽  
A. Fernandez ◽  
C. del Rio Martinez
Keyword(s):  
Angiotensin Converting Enzyme ◽  
Brush Border ◽  
Physiological Role ◽  
Intestinal Epithelial ◽  
Converting Enzyme ◽  
Brush Border Membranes ◽  
Fluid Uptake ◽  
The Common ◽  
Kinetics Of ◽  
Hydrolysis Of

Angiotensin converting enzyme activity was identified in brush-border membranes purified from the small intestinal epithelium of the common grackle, Quiscalus quiscula. Angiotensin converting enzyme was enriched 20-fold in the membrane preparation, compared with intestinal epithelial cell scrapes, and was coenriched with the brush-border markers, alkaline phosphatase and aminopeptidase N. The kinetics of hydrolysis of N-[3-(2-furyl)acryloyl]-L-phenylalanylglycylglycine (FAPGG) gave a Vmax of 907 +/− 41 units g-1 and a Km of 55 +/− 6 mumol l-1. The avian intestinal angiotensin converting enzyme was inhibited by the antihypertensive drug, Ramipril, with a median inhibitory concentration (IC50) of 1 nmol l-1. In the light of previous studies on angiotensin converting enzyme in mammalian epithelia, these results may implicate a physiological role for angiotensin converting enzyme in regulating electrolyte and fluid uptake in bird small intestines.

scholarly journals Angiotensin Converting Enzyme Activity in Compensatory Renal Hypertrophy

2007 ◽  
Vol 7 (1) ◽  
pp. 79-83 ◽  
Author(s):  
Nermina Babić ◽  
Jasminko Huskić ◽  
Emina Nakaš-Ićindić
Keyword(s):  
Enzymatic Hydrolysis ◽  
Angiotensin Converting Enzyme ◽  
Hippuric Acid ◽  
Unilateral Nephrectomy ◽  
Converting Enzyme ◽  
Compensatory Mechanisms ◽  
Renal Hypertrophy ◽  
Serum Activity ◽  
Ace Activity ◽  
Hydrolysis Of

Serum and tissue (kidney's) angiotensin-converting enzyme (ACE) activity has been examined in Wistar rats (10 males and 10 females), seven days after unilateral nephrectomy. Renal hypertrophy was determined by measurement of kidney absolute mass. Serum and tissue ACE activity was determined by spectrophotometric method using hippuryl-l-histidyl-l-leucine (Hip-His-Leu) as a substrate. The ACE serum activity was expressed in units that correspond to 1 nmol of hippuric acid released by enzymatic hydrolysis of Hip-His-Leu substrate per minute/ml serum. The ACE tissue activity was expressed in units that correspond to 1 nmol of hippuric acid released by enzymatic hydrolysis of Hip-His-Leu substrate per minute/mg protein or mg kidney's tissue. The ACE serum activity significantly increased (p<0,05) seven days after unilateral nephrectomy. The ACE tissue activity, expressed in units that corresponds to 1 nmol of hippuric acid released by hydrolysis of Hip-His-Leu substrate per minute/mg protein, was higher seven days after unilateral nephrectomy then in kidney control, but the difference was not significant compared to the values determined in kidney control. The ACE tissue activity, expressed in units that correspond to 1 nmol of hippuric acid released by hydrolysis of Hip-His-Leu substrate per minute/mg tissue, was increased seven days after unilateral nephrectomy, which is statistically significant compared to the activity of the same enzyme in kidney control (p<0,01). The results indicate that ACE, probably has an important role in development of adaptive compensatory mechanisms after unilateral nephrectomy.

scholarly journals Novel activity of angiotensin-converting enzyme. Hydrolysis of cholecystokinin and gastrin analogues with release of the amidated C-terminal dipeptide

1989 ◽  
Vol 262 (1) ◽  
pp. 125-130 ◽  
Author(s):  
P Dubreuil ◽  
P Fulcrand ◽  
M Rodriguez ◽  
H Fulcrand ◽  
J Laur ◽  
...  
Keyword(s):  
Angiotensin Converting Enzyme ◽  
Chloride Ion ◽  
Peptide Bond ◽  
Major Product ◽  
Enzyme Hydrolysis ◽  
Ion Concentration ◽  
Converting Enzyme ◽  
Rabbit Lung ◽  
Hydrolysis Of

ACE (angiotensin-converting enzyme; peptidyl dipeptidase A; EC 3.4.15.1), cleaves C-terminal dipeptides from active peptides containing a free C-terminus. We investigated the hydrolysis of cholecystokinin-8 [CCK-8; Asp-Tyr(SO3H)-Met-Gly-Trp-Met-Asp-Phe-NH2] and of various gastrin analogues by purified rabbit lung ACE. Although these peptides are amidated at their C-terminal end, they were metabolized by ACE to several peptide fragments. These fragments were analysed by h.p.l.c., isolated and identified by comparison with synthetic fragments, and by amino acid analysis. The initial and major site of hydrolysis was the penultimate peptide bond, which generated a major product, the C-terminal amidated dipeptide Asp-Phe-NH2. As a secondary cleavage, ACE subsequently released di- or tri-peptides from the C-terminal end of the remaining N-terminal fragments. The cleavage of CCK-8 and gastrin analogues was inhibited by ACE inhibitors (Captopril and EDTA), but not by other enzyme inhibitors (phosphoramidon, thiorphan, bestatin etc.). Hydrolysis of [Leu15]gastrin-(14-17)-peptide [Boc (t-butoxycarbonyl)-Trp-Leu-Asp-Phe-NH2] in the presence of ACE was found to be dependent on the chloride-ion concentration. Km values for the hydrolysis of CCK-8, [Leu15]gastrin-(11-17)-peptide and Boc-[Leu15]gastrin-(14-17)-peptide at an NaCl concentration of 300 mM were respectively 115, 420 and 3280 microM, and the catalytic constants were about 33, 115 and 885 min-1. The kcat/Km for the reactions at 37 degrees C was approx. 0.28 microM-1.min-1, which is approx. 35 times less than that reported for the cleavage of angiotensin I. These results suggest that ACE might be involved in the metabolism in vivo of CCK and gastrin short fragments.

scholarly journals Kinetic probes for inter-domain co-operation in human somatic angiotensin-converting enzyme

2005 ◽  
Vol 391 (3) ◽  
pp. 641-647 ◽  
Author(s):  
Olga E. Skirgello ◽  
Peter V. Binevski ◽  
Vladimir F. Pozdnev ◽  
Olga A. Kost
Keyword(s):  
Angiotensin Converting Enzyme ◽  
Enzymatic Activity ◽  
Active Site ◽  
The Other ◽  
Converting Enzyme ◽  
Human Enzyme ◽  
Independent Functions ◽  
The Common ◽  
The Individual ◽  
Hydrolysis Of

s-ACE (the somatic form of angiotensin-converting enzyme) consists of two homologous domains (N- and C-domains), each bearing a catalytic site. Negative co-operativity between the two domains has been demonstrated for cow and pig ACEs. However, for the human enzyme there are conflicting reports in the literature: some suggest possible negative co-operativity between the domains, whereas others indicate independent functions of the domains within s-ACE. We demonstrate here that a 1:1 stoichiometry for the binding of the common ACE inhibitors, captopril and lisinopril, to human s-ACE is enough to abolish enzymatic activity towards FA {N-[3-(2-furyl)acryloyl]}-Phe-GlyGly, Cbz (benzyloxycarbonyl)-Phe-His-Leu or Hip (N-benzoylglycyl)-His-Leu. The kinetic parameters for the hydrolysis of seven tripeptide substrates by human s-ACE appeared to represent average values for parameters obtained for the individual N- and C-domains. Kinetic analysis of the simultaneous hydrolysis of two substrates, Hip-His-Leu (S1) and Cbz-Phe-His-Leu (S2), with a common product (His-Leu) by s-ACE at different values for the ratio of the initial concentrations of these substrates (i.e. σ=[S2]0/[S1]0) demonstrated competition of these substrates for binding to the s-ACE molecule, i.e. binding of a substrate at one active site makes the other site unavailable for either the same or a different substrate. Thus the two domains within human s-ACE exhibit strong negative co-operativity upon binding of common inhibitors and in the hydrolysis reactions of tripeptide substrates.

scholarly journals Hydrolysis of Biological Peptides by Human Angiotensin-converting Enzyme-related Carboxypeptidase

2002 ◽  
Vol 277 (17) ◽  
pp. 14838-14843 ◽  
Author(s):  
Chad Vickers ◽  
Paul Hales ◽  
Virendar Kaushik ◽  
Larry Dick ◽  
James Gavin ◽  
...  
Keyword(s):  
Angiotensin Converting Enzyme ◽  
Converting Enzyme ◽  
Hydrolysis Of
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