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Species Differences in the Binding of [ 3 H]Nitrobenzylthioinosine to the Nucleoside Transport System in Mammalian Central Nervous System Membranes: Evidence for Interconvertible Conformations of the Binding Site/Transporter Complex
Author(s) -
Hammond James R.,
Clanachan Alexander S.
Publication year - 1985
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1985.tb04020.x
Subject(s) - nucleoside transporter , nucleoside , transporter , membrane , chemistry , membrane transport , binding site , biophysics , central nervous system , organic cation transport proteins , membrane transport protein , biochemistry , biology , neuroscience , membrane protein , gene
The binding of [ 3 H]nitrobenzylthioinosine (NBMPR) to specific sites in CNS membranes was investigated using cortical tissue from a variety of mammalian species. Mass law analysis of the site‐specific binding of NBMPR data revealed that rat, mouse, guinea pig, and dog cortical membranes each contained an apparent single class of high‐affinity ( K D 0.11–4.9 n M ) binding sites for NBMPR; rabbit cortical membranes, however, exhibited two distinct classes of NBMPR binding sites with K D values of 0.4 n M and 13.8 n M. Dipyridamole, a potent inhibitor of nucleoside transport, produced a biphasic profile of inhibition of the binding of NBMPR to guinea pig, rabbit, and dog membranes (IC 50 < 20 n M and IC 50 > 6 μ M for NBMPR binding sites displaying high and low affinity for dipyridamole, respectively). These results are indicative of heterogeneity of NBMPR binding sites in mammalian cortical membranes. Rat and mouse cortical membranes appear to possess only one type of NBMPR binding site, which has low affinity for dipyridamole. Detailed analysis of inhibitorinduced dissociation of NBMPR from its sites in each species led to the conclusion that these multiple forms of NBMPR binding sites are different conformations of a single site associated with the CNS nucleoside transport system, rather than two distinct sites. It is also suggested that the affinity of dipyridamole for each conformation of NBMPR site indicates the susceptibility of that conformation of the nucleoside transport system to inhibition by dipyridamole.