Enkephalin-degrading dipeptidyl carboxypeptidase in guinea pig serum: its properties and action on bioactive peptides

Identification of protein fold topology shared between different folds inhibited by natural products

Natural products have withstood the test of time as therapeutics, but new lead-generation strategies have focussed away from natural products. A new approach that uses natural-product recognition to drive an understanding of biological space might provide an impetus for renewed focus on natural-product starting points. Protein fold topology (PFT) has been shown to be an underlying factor for natural-product recognition. An investigation of natural product inhibitors of the Zincin-like fold has demonstrated their capacity also to inhibit targets of different fold types. Analysis of crystal structure complexes for natural products cocrystallised within different fold types has shown similarity at the PFT level. Two new PFT(T) (where subscript T denotes PFT shared between therapeutic targets) relationships have been established: the Zincin-like- metallohydrolase/oxidoreductase PFT(T) and the Zincin-like-phosphorylase/hydrolase PFT(T). The PFT relationship between a natural product's biosynthetic enzyme and therapeutic target, and now between different fold targets of the same natural product, suggests that PFT is the simplest descriptor of biological space. This fundamental factor for recognition could facilitate a rational approach to drug development guided by natural products.

Enkephalin-degrading enzymes and their inhibitors in human saliva

The possible presence of enzymes able to hydrolyze leucine enkephalin has been investigated in human saliva. The data obtained indicate that, in the presence of saliva, Leu-enkephalin is partially hydrolyzed. The disappearance of the substrate is paired with the formation of hydrolysis byproducts whose composition indicates the presence of all three classes of enzymes known to hydrolyze enkephalins: aminopeptidases, dipeptidylaminopeptidases, and dipeptidylcarboxypeptidases. The presence of low molecular weight substances with inhibitory activity on proteolytic enzymes has also been detected. These substances are active on all three classes of enkephalin-degrading enzymes, although the inhibition is more evident on dipeptidylpeptidases than on aminopeptidases. Substrate degradation was found to be higher in male than in female saliva: this seems to be caused by the activities both of enzymes and low molecular weight inhibitors that are different in the two sexes.

Enkephalin-degrading dipeptidylcarboxypeptidases in human and Cavia porcellus plasma

1. The dipeptidylcarboxypeptidases that degrade leucine enkephalin in human and guinea pig plasma were studied by kinetic and chromatographic techniques. 2. The extremely rapid degradation of enkephalins in Cavia plasma seems to be caused by both increased activity of enzymes and reduced role of inhibitors. 3. The increased role of dipeptidylcarboxypeptidases in Cavia as compared to Homo appears prevalently caused by the presence in the former species of a considerable number of very active enzymes. 4. The sum of these data indicates the existence of noticeable intraspecific differences either in peptide-degrading enzymes present in plasma, or in plasma peptides, or in both.

Prevention of cold-induced increase in blood pressure of rats by captopril

To assess the possibility that the renin-angiotensin system may play a role in the development of cold-induced hypertension, three groups of rats were used. Two groups were exposed to cold (5 +/- 2 degrees C) while the remaining group was kept at 26 +/- 2 degrees C. One group of cold-treated rats received food into which captopril (0.06% by weight) had been thoroughly mixed. The remaining two groups received the same food but without captopril. Systolic blood pressure of the untreated, cold-exposed group increased significantly above that of the warm-adapted, control group within 4 weeks of exposure to cold. In contrast, chronic treatment with captopril prevented the elevation of blood pressure. Rats were killed after 4 months of exposure to cold. At death, the heart, kidneys, adrenal glands, and interscapular brown fat pad were removed and weighed. Although captopril prevented the elevation of blood pressure in cold-treated rats, it did not prevent hypertrophy of the kidneys, heart, and interstitial brown adipose tissue that characteristically accompanies exposure to cold. Thus, chronic treatment with captopril prevented the elevation of blood pressure when administered at the time exposure to cold was initiated. It also reduced the elevated blood pressure of cold-treated rats when administered after blood pressure became elevated. This suggests that the renin-angiotensin system may play a role in the elevation of blood pressure during exposure to cold.

Changes in blood pressure and dipsogenic responsiveness to angiotensin II during chronic exposure of rats to cold

Hypertension accompanies chronic exposure of rats to cold (5-6 degrees C). Systolic, diastolic, and mean blood pressures become elevated, and hypertrophy of the heart occurs. A previous study from this laboratory suggested that the renin-angiotensin system may play a role. The present study was carried out to assess this further. Thus, in addition to measurement of systolic blood pressure at intervals during exposure to cold, plasma renin activity and the dipsogenic responsiveness to acute administration of angiotensin II were also measured to assess the functional status of the renin-angiotensin system. The results showed a significant (p less than 0.05) increase in systolic blood pressure during the third week of exposure to cold. In contrast, plasma renin activity (PRA) increased within the first week of exposure to cold, and declined thereafter to reach the level of the control by the third week of exposure to cold. By the fourth week, PRA decreased to a level significantly (p less than 0.05) below that of the control group. The responsiveness to acute administration of angiotensin II (AII), as assessed by the drinking response, increased significantly (p less than 0.05) by the third week of exposure to cold and remained significantly elevated during the fourth week. There was a significant (p less than 0.01) direct relationship between dipsogenic responsiveness to AII and blood pressure in the cold-treated (r = .57), but not the control group (r = .12). There was also a significant (r = -.91) indirect linear relationship between PRA and dipsogenic responsiveness to AII. Cold-treated rats had significant increases in urinary norepinephrine output and weights of heart, kidneys, adrenals, and brown adipose tissue characteristic of rats acclimated to cold.(ABSTRACT TRUNCATED AT 250 WORDS)

Hydrolysis of neo-kyotorphin (Thr-Ser-Lys-Tyr-Arg) and [Met]enkephalin-Arg6-Phe7 by angiotensin-converting enzyme from monkey brain

Angiotensin-converting enzyme (ACE; dipeptidyl carboxypeptidase, EC 3.4.15.1) from monkey brain was partially purified 274-fold with 4.5% yield. The optimum pH of the enzyme was 8.2, and its Km was 3.3 mM, with hippuryl-His-Leu as the substrate in 300 mM NaCl. Its molecular weight (Mr) was estimated to be approximately 260,000 by gel filtration on Sephadex G-200. On high-performance liquid chromatographic analysis, ACE hydrolyzed neo-kyotorphin Thr-Ser-Lys-Tyr-Arg) with liberation of kyotorphin (Tyr-Arg), the [Met]enkephalin releaser. ACE also converted [Met]enkephalin-Arg6-Phe7 to [Met]enkephalin; then the enzyme slowly hydrolyzed the resulting [Met]enkephalin. The Km values of the enzyme for neo-kyotorphin and [Met]enkephalin-Arg6-Phe7 were 0.58 and 0.30 mM respectively. Thus, brain ACE may have a role in the formation of kyotorphin and [Met]enkephalin from their precursors but has little part in [Met]enkephalin degrading processes.

Isolation of angiotensin-converting enzyme inhibitor from porcine plasma

An inhibitory peptide of angiotensin-converting enzyme was purified from porcine plasma. The final preparation showed IC50 values of 4.2, 0.6, and 0.9 microgram/ml for angiotensin-converting enzymes from guinea pig serum, rabbit lung, and monkey brain, respectively. The amino acid sequence of the inhibitor was determined as leucyl-valyl-leucine by Edman procedure. This structural observation was supported by mass spectrometric analysis.