Fe(2+)-mediated binding of serotonin and dopamine to skeletal muscle actin: resemblance to serotonin binding proteins.
Fe2+ stimulates the binding of [3H]serotonin and [3H]dopamine to rabbit skeletal muscle actin. This binding is inhibited by reducing agents (sodium ascorbate, vitamin E), by superoxide dismutase and by sulfhydryl group-modifying reagents (N-ethyl-maleimide, 2,2'-dinitro-5,5'-dithiobenzoic acid). The effect of Fe2+ is mimicked by oxidants (sodium periodate, potassium nitroso-disulfonate) and by superoxide radicals. Once formed, the binding cannot be decreased by a large excess of monoamine. It is proposed that Fe2+ catalyses the autoxidation of the monoamines by generating oxygen free radicals, and the oxidation products are likely to bind covalently to exposed cysteine residues of actin. Digestion of [3H]dopamine-labelled actin by cyanogen bromide and then by V8 protease (EC3.4.21.19) yields two labelled peptides whose apparent molecular weights (4.1 and 1.2 kDa) are compatible with the labelling of cysteine-10 and -374. Fe2+ also inactivates some of the binding sites on actin. This inactivation, and the covalent nature of the binding precludes the interpretation of monoamine saturation and competition binding data in terms of reversible bimolecular interactions.
Velez Pardo
C
C
Department of Protein Chemistry, Free University Brussels (V.U.B.), St. Genesius-Rode Belgium.
Jimenez del Rio
M
M
Pinxteren
J
J
De Potter
W
W
Ebinger
G
G
Vauquelin
G
G
D000199:Actins / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D003488:Cyanogen Bromide; D004298:Dopamine / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D006868:Hydrolysis; D007501:Iron / Q000502:physiology*; D018482:Muscle, Skeletal / Q000378:metabolism*; D010455:Peptides / Q000032:analysis; D011485:Protein Binding; D011817:Rabbits; D012697:Serine Endopeptidases; D012701:Serotonin / Q000378:metabolism*
D000199:Actins; D002352:Carrier Proteins; D010455:Peptides; C025366:serotonin-binding protein; D012701:Serotonin; D007501:Iron; D012697:Serine Endopeptidases; C028344:glutamyl endopeptidase; D003488:Cyanogen Bromide; D004298:Dopamine