Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.24.27 (thermolysin)
 1,894 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The functional and biochemical characteristics of somatostatin (somatotropin release-inhibiting factor) (SRIF) receptor subtypes were examined in the clonal pituitary cell lines AtT-20 and GH3. SRIF inhibits evoked calcium influx into each of these cell lines. The rank order of potencies of structural analogues of SRIF to inhibit calcium influx into GH3 versus AtT-20 cells was different. Inhibitory actions of SRIF on calcium influx desensitized in AtT-20 cells but not GH3 cells. The biochemical properties of the SRIF receptor subtypes in AtT-20 and GH3 cells were assessed by photoaffinity labeling of each receptor with the nonreducible SRIF analogue [125I]CGP 23996 and the photocrosslinking agent n-hydroxysuccinimidyl-4-azidobenzoate. The covalently labeled receptors in both cell lines had the same size, 55 +/- 5 kDa, as assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The covalent binding of [125I]CGP-23996 to GH3 and AtT-20 cell membranes was blocked by 1 microM SRIF, somatostatin 28, Trp8-SRIF and was GTP sensitive. Analysis of the labeled receptors in GH3 and AtT-20 cell membranes by two-dimensional polyacrylamide gel electrophoresis indicated that they were of similar charge (pI = 6-6.5) and that they comigrate when applied together. Proteolysis of the GH3 and AtT-20 cell SRIF receptors with Staphylococcus aureus V-8 and thermolysin revealed similar peptide maps. Pretreatment of AtT-20 cells with different stable SRIF analogues abolished the subsequent equilibrium or covalent labeling of the SRIF receptor with [125I]CGP-23996. Similar treatment of GH3 cells did not reduce the covalent labeling of the SRIF receptor by [125I]CGP 23996. These studies indicate that the functional characteristics of SRIF receptors in GH3 and AtT-20 cells are different. However, clear differences in the biochemical properties of these receptor subtypes were not observed. Subtle variations in the structure of the SRIF receptors may therefore be responsible for the functional differences.
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PMID:Somatostatin receptor subtypes in the clonal anterior pituitary cell lines AtT-20 and GH3. 289 89

Peptide hormone inactivating endopeptidase (PHIE) is a metalloendopeptidase which was isolated from the skin granular gland secretions of Xenopus laevis [Carvalho, K. M., Joudiou, C., Boussetta, H., Leseney, A. M., & Cohen, P. (1992) Proc. Natl. Acad. Sci. U.S.A. 89, 84-88]. This peptidase exhibits a thermolysin-like character and hydrolyzes bonds on the amino terminus of hydrophobic amino acids, performing cleavage of Xaa-Phe, Xaa-Leu, Xaa-Ile, Xaa-Tyr, and Xaa-Trp doublets. When the enzyme recognized a doublet of hydrophobic amino acids such as Phe6-Phe7 of somatostatin-14, Phe7-Phe8 of substance P, Phe4-Leu5 of [Leu5,Arg6]enkephalin, and Tyr4-Ile5 of angiotensin II, cleavage occurred preferentially between these residues. The use of selectively modified carboxy-terminal octapeptide fragments of atrial natriuretic factor (ANF) indicated that the enzyme tolerates as substrates only peptides bearing a P'1 bulky hydrophobic amino acid residue. Although a P'1 hydrophobic residue was a necessary condition, it was found in a number of peptides that all potential cleavage sites were not recognized by the enzyme. These data suggested that this metalloendoprotease requires for its thermolysin-like activity a preferred conformation of the peptide chain. Kinetic results obtained using a series of related substrates derived from biologically active peptides of the atrial natriuretic factor, tachykinin, and enkephalin families indicated the presence of an extended binding site accommodating at least six amino acid residues, in contrast to thermolysin (EC 3.4.24.4) and neutral endopeptidase (NEP; EC 3.4.24.11), which hydrolyze shorter homologous peptides.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Characterization of the thermolysin-like cleavage of biologically active peptides by Xenopus laevis peptide hormone inactivating enzyme. 850 36