The dopamine transporter and cytochrome P45OIID1 (debrisoquine 4-hydroxylase) in brain: resolution and identification of two distinct [3H]GBR-12935 binding proteins.
Two [3H]GBR-12935 binding proteins, identified as the dopamine transporter and cytochrome P45OIID1, were solubilized in digitonin from canine striatal membranes, and were resolved following wheat germ agglutinin (WGA)-lectin column chromatography. Protein adsorbed to and specifically eluted from WGA-lectin with N-acetylglucosamine displayed saturable, high affinity (KD approximately 3 nM), and sodium-dependent binding of [3H]GBR-12935, which was inhibited in a concentration-dependent and stereoselective manner by dopamine uptake blockers and substrates with a pharmacological profile indicative of the dopamine uptake site. Protein not adsorbed to WGA-lectin also bound [3H]-GBR-12935 with high affinity (approximately 7 nM), in a sodium-independent manner, and was insensitive to classical dopamine uptake blockers and substrates such as mazindol or dopamine, corresponding to the so-called "piperazine acceptor" site seen in native membranes. [3H]GBR-12935 binding to this latter protein was, however, inhibited by various compounds with a pharmacological profile indicative of a form of cytochrome P450 designated P45OIID1 (debrisoquine/sparteine monooxygenase) with the following rank order of inhibitory potency: GBR-12909 greater than budipine greater than alpha-lobeline greater than quinidine greater than alpha flupenthixol greater than SKF-525A greater than sparteine greater than quinine. Ki values obtained for inhibition of [3H]-GBR-12935 binding to neuronal WGA passthrough fractions by these drugs correlate well with their respective Ki values for liver P45OIID1 activity. Western blotting and immunoprecipitation analysis with rabbit anti-rat P45OIID1 antibody also supported the identity of the mazindol-insensitive [3H]GBR-12935 binding site (or piperazine acceptor site) as P45OIID1. Furthermore, a [3H]GBR-12935 binding protein with pharmacological and immunological characteristics similar to those of P45OIID1 was solubilized from both bovine and human liver membranes, and GBR-12909 was found to be a potent competitive inhibitor (Ki approximately 100 nM) of sparteine monooxygenase activity in human liver microsomes. These data clearly indicate that [3H]GBR-12935 and its analogs display similar affinities for both the dopamine transporter and neuronal P45OIID1, and that this radioligand may be a useful probe of P45OIID1 activity in brain and liver. The exact molecular and functional association (if any) between these two distinct binding protein populations remains to be established; however, it is tempting to speculate that P45OIID1 is involved in the catabolism and processing of neurotransmitters subsequent to their reuptake into target cells.
Niznik
H B
HB
Department of Psychiatry, University of Toronto, Ontario, Canada.
Tyndale
R F
RF
Sallee
F R
FR
Gonzalez
F J
FJ
Hardwick
J P
JP
Inaba
T
T
Kalow
W
W
D000818:Animals; D001667:Binding, Competitive; D002352:Carrier Proteins / Q000302:isolation & purification / Q000378:metabolism*; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism; D002846:Chromatography, Affinity; D003342:Corpus Striatum / Q000378:metabolism*; D019389:Cytochrome P-450 CYP2D6; D003577:Cytochrome P-450 Enzyme System / Q000302:isolation & purification / Q000378:metabolism*; D004285:Dogs; D004298:Dopamine / Q000378:metabolism*; D050483:Dopamine Plasma Membrane Transport Proteins; D007700:Kinetics; D008024:Ligands; D008099:Liver / Q000378:metabolism*; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D008862:Microsomes, Liver / Q000201:enzymology; D006899:Mixed Function Oxygenases / Q000302:isolation & purification / Q000378:metabolism*; D009419:Nerve Tissue Proteins; D010879:Piperazines / Q000378:metabolism*
D002352:Carrier Proteins; D050483:Dopamine Plasma Membrane Transport Proteins; D008024:Ligands; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D010879:Piperazines; D003577:Cytochrome P-450 Enzyme System; C044630:1-(2 (diphenylmethoxy)ethyl)-4-(3-phenylpropyl)piperazine; D006899:Mixed Function Oxygenases; D019389:Cytochrome P-450 CYP2D6; D004298:Dopamine