High-affinity formation of a 2:1 complex between gramicidin S and calmodulin.

High-affinity formation of a 2:1 complex between gramicidin S and calmodulin. Research Abstract Details 

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High-affinity formation of a 2:1 complex between gramicidin S and calmodulin. Abstract Text:

J A Cox,M Milos,M Comte,

Two molecules of gramicidin S, a very rigid cyclic decapeptide rich in beta-sheet structure, can bind in a Ca2+-dependent way to a calmodulin molecule in the presence as well as in the absence of 4 M-urea. The flow-microcalorimetric titration of 25 microM-calmodulin with gramicidin S at 25 degrees C is endothermic for 21.3 kJ.mol-1; the enthalpy change is strictly linear up to a ratio of 2, indicating that the affinity constant for binding of the second gramicidin S is at least 10(7) M-1. In 4 M-urea the peptide quantitatively displaces seminalplasmin from calmodulin, as monitored by tryptophan fluorescence. An iterative data treatment of these competition experiments revealed strong positive co-operativity with K1 less than 5 X 10(5) M-1 and K1.K2 = 2.8 X 10(12) M-2. A competition assay with the use of immobilized melittin enabled us to monitor separately the binding of the second gramicidin S molecule: the K2 value is 1.9 X 10(7) M-1. By complementarity, the K1 value is 1.5 X 10(5) M-1. In the absence of urea the seminalplasmin displacement is incomplete: the data analysis shows optimal fitting with K1 less than 2 X 10(4) M-1 and K1.K2 = 3.2 X 10(11) M-2 and reveals that the mixed complex (calmodulin-seminalplasmin-gramicidin S) is quite stable and is even not fully displaced from calmodulin at high concentrations of gramicidin S. The activation of bovine brain phosphodiesterase by calmodulin is not impaired up to 0.2 microM-gramicidin S. According to our model the ternary complex enzyme-calmodulin-gramicidin is relatively important and displays the same activity as the binary complex enzyme-calmodulin. Gramicidin S also displaces melittin from calmodulin synergistically, as monitored by c.d. Our studies with gramicidin S reveal the importance of multipoint attachments in interactions involving calmodulin and confirm the heterotropic co-operativity in the binding of calmodulin antagonists first demonstrated by Johnson [(1983) Biochem. Biophys. Res. Commun. 112, 787-793].

High-affinity formation of a 2:1 complex between gramicidin S and calmodulin. Publishing Authors By Initials

JA Cox,M Milos,M Comte,

For similar natural sciences: physics: thermodynamics research abstracts see: natural sciences: physics: thermodynamics research

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High-affinity formation of a 2:1 complex between gramicidin S and calmodulin. Journal Published:

PUBLICATION TYPE: Research Support, Non-U.S. Gov

Journal: The Biochemical journal

VOLUME: 246

Page Numbers: 495-502

Journal Abbreviation: Biochem. J.

ISSN: 0264-6021

DAY: 1

MONTH: Sep

YEAR: 1987

High-affinity formation of a 2:1 complex between gramicidin S and calmodulin. Information

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LANGUAGE: eng

NlmUniqueID: 2984726

High-affinity formation of a 2:1 complex between gramicidin S and calmodulin. Keywords Mesh Terms:

KEYWORDS: Thermodynamics

MESH TERMS: metabolism

Chemical & Substance for Abstract: High-affinity formation of a 2:1 complex between gramicidin S and calmodulin. Information

Substance Name: 2',3'-Cyclic-Nucleotide Phosphodiesteras

Registry Number: EC 3.1.4.-

Grant and Affiliation Information for High-affinity formation of a 2:1 complex between gramicidin S and calmodulin.

AFFILIATION: Department of Biochemistry, University of Geneva, Switzerland.

Country: ENGLAND

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MEDLINETA: Biochem J

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