Abstract
Nipecotic acid is one of the most potent competitive inhibitors and alternative substrates for the high-affinity γ-aminobutyric acid transport system in neurons, but the structural basis of this potency is unclear. Because γ-aminobutyrate is a highly flexible molecule in solution, it would be expected to lose rotational entropy upon binding to the transport system, a change which does not favor binding. Nipecotic acid, in contrast, is a much less flexible molecule, and one would expect the loss of conformational entropy upon binding to be smaller thus favoring the binding of nipecotic acid over γ-aminobutyric acid. To investigate this possibility, the thermodynamic parameters, ΔG°, ΔH°, and ΔS°, were determined for the binding of γ-aminobutyrate and nipecotic acid to the high affinity GABA transport system in synaptosomes. In keeping with expectations, the apparent entropy change for nipecotic acid binding (112±13 J·K−1) was more favorable than the apparent entropy change for γ-aminobutyric acid binding (61.3±6.6 J·K−1). The results suggest that restricted conformation per se is an important contributory factor to the affinity of nipecotic acid for the high-affinity transport system for γ-aminobutyric acid.
Similar content being viewed by others
References
Brehm, L., Krogsgaard-Larsen, P., and Jacobsen, P. 1979. GABA uptake inhibitors and structurally related “pro-drugs,” Page 247–262,in Krogsgaard-Larsen, P., Scheel-Kruger, J. K. and Kofod, H. (eds). GABA-Neurotransmitters: Pharmacochemical, Biochemical and Pharmacological Aspects, Academic Press, New York.
Johnston, G. A. R., Stephanson, A. L., and Twitchin, B. 1976. Uptake and release of nipecotic acid by rat brain slices. J. Neurochem. 26:83–87.
Krogsgaard-Larsen, P. and Johnston, G. A. R. 1975. Inhibition of GABA uptake in rat brain slices by nipecotic acid, various isoxazoles and related compounds. J. Neurochem. 25:797–802.
Kovalev, G. I., and Raevskii, K. S. 1981. Nipecotic acid, a competitive inhibitor of3H-GABA net uptake by rat brain synaptosomes. Bull. Exp. Biol. Med. 91:764–766.
Larsson, O. M., Krogsgaard-Larsen, P., and Schousboe, A., 1980. High-affinity uptake of (RS)-nipecotic acid in astrocytes cultured from mouse brain. Comparison with GABA transport. J. Neurochem. 34:970–977.
Larsson, O. M., Drejer, J., Hertz, L., and Schousboe, A. 1983. Ion dependency of uptake and release of GABA and (RS)-nipecotic acid studied in cultured mouse brain cortex neurons. J. Neurosci. Res. 9:291–302.
Minchin, M. C. W. 1979. Uptake of [14C]nipecotic acid into rat dorsal root ganglia. J. Neurochem. 32:1519–1524.
Brehm, L., Krogsgaard-Larsen, P., Johnston, G. A. R., and Schaumburg, K. 1976. X-ray crystallographic and proton magnetic resonance spectroscopic investigations of nipecotic acid, a potent inhibitor of γ-aminobutyric acid (GABA) uptake. Acta Chem. Scand. 30:542–548.
Johnston, G. A. R., Allan, R. D., Kennedy, S. M. E., and Twitchin, B. 1976. Systematic study of GABA analogues of restricted conformation. Pages 149–164,in Krogsgaard-Larsen, P., Scheel-Kruger, J. K. and Kofod, H. (eds.) GABA-Neurotransmitters. Pharmacochemical, Biochemical and Pharmacological Aspects. Academic Press, New York.
Ham, N. S. 1974. NMR studies of solution conformations of physiologically active amino acids. Pages 256–263,in Bergmann E. and Pullman, B. (eds.). Molecular and Quantum Pharmacology. D. Reidel, Dordrecht-Holland.
Quitt, J., Hellerbach, Q. J. and Vogler, K. 1963. Synthesis of optically active IV-monomethylamino acids. Helv. Chim. Acta. 46:327–333.
Freifelder, M. 1963. A simple preparation of nipecotic acid. J. Org. Chem. 28:1135.
Whittaker, V. P. Synaptosomes, Pages 327–364,in Lajtha, A. (ed.) Handbook of Neurochemistry. Plenum Press, New York.
Vargas, F., and Erlig, D. 1976. The effects of harmaline on GABA fluxes in pinched-off nerve endings. Brain Res. 113:611–615.
Martin, D. L. 1976. Carrier-mediated transport and removal of GABA from synaptic regions. Pages 347–386,in Roberts, E., Chase, T. N., and Tower, D. B. (eds.). GABA in Nervous System Function. Raven Press, New York.
Eisenthal, R., and Cornish-Bowden, A. 1974. A new graphical procedure for estimating enzyme kinetic parameters. Biochem. J. 139:715–720.
Althaus, J. S., and Martin, D. L. 1985. Application of the median method to the determination of kinetic constants for competitive enzyme inhibition. Analyt. Biochem. 151:254–262.
Marshall, A. G. 1978. Biophysical Chemistry, Wiley, New York.
Simon, J. R., Martin, D. L., and Kroll, M. 1974. Sodium-dependent efflux and exchange of GABA in synaptosomes. J. Neurochem. 23:981–991.
Johnston, G. A. R., Krogsgaard-Larsen, P., Stephanson, A. L., and Twitchin, B. 1976. Inhibition of the uptake of GABA and related amino acids in rat brain slices by the optical isomers of nipecotic acid. J. Neurochem. 26:1029–1032.
Page, M. I., and Jencks, W. P. 1971. Entropic contributions to rate accelerations in enzymic and intramolecular reactions and the chelate effect. Proc. Natl. Acad. Sci. USA, 68:1678–1683.
Segel, I. H. 1978. Enzyme Kinetics, John Wiley and Sons, New York.
Falke, J. J., Kanes, K. J., and Chan, S. I. 1985. The kinetic equation for the chloride transport cycle of band 3. J. Biol. Chem. 260:9545–9551.
May, J. M. and Mikulecky, D. C. 1982. A simple model of adipocyte hexose transport. J. Biol. Chem. 257:11601–11608.
Sidhu, H. S., and Wood, J. D. 1986. Three uptake systems in synaptosomes for nipecotic acid and beta-alanine. Neuropharmacol. 25:555–558.
Author information
Authors and Affiliations
Additional information
Special issue dedicated to Dr. Elling Kvamme.
This work was conducted when both authors were at the Department of Chemistry, University of Maryland, College Park.
Rights and permissions
About this article
Cite this article
Althaus, J.S., Martin, D.L. Entropy as a factor in the binding of γ-aminobutyric acid and nipecotic acid to the γ-aminobutyric acid transport system. Neurochem Res 14, 311–316 (1989). https://doi.org/10.1007/BF01000032
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF01000032