RESUMEN
Subfragment-1 of rabbit atrial and thyrotoxic ventricular myosin (V1 isomyosin) has been prepared and purified by DEAE-cellulose column chromatography. Pyrophosphate-polyacrylamide gel electrophoretic patterns and column chromatographic profile of the atrial subfragment differ from those of thyrotoxic ventricular myosin subfragment-1. On the other hand, Ca2+, Mg2+ and actin-activated ATPase activities of these subfragments are identical. Comparison of the peptide mapping by limited proteolysis in the presence of sodium dodecyl sulfate of the heavy and the light subunits of these subfragments reveals that the patterns for the heavy chain peptides of these subfragments are substantially similar but their light chain peptide patterns differ. The results suggest that the enzymatic and structural similarities that have been recognized between these isoenzymes using intact myosin hold true for the myosin subfragment-1. The differences between these subfragments are due to the differences in the light chains associated with them.
Asunto(s)
Miocardio/enzimología , Miosinas/metabolismo , Fragmentos de Péptidos/metabolismo , Tirotoxicosis/enzimología , Animales , ATPasa de Ca(2+) y Mg(2+)/metabolismo , ATPasas Transportadoras de Calcio/metabolismo , Electroforesis en Gel de Poliacrilamida , Atrios Cardíacos/enzimología , Ventrículos Cardíacos/enzimología , Cinética , Subfragmentos de Miosina , Miosinas/aislamiento & purificación , Fragmentos de Péptidos/aislamiento & purificación , Mapeo Peptídico , Conejos , Valores de ReferenciaRESUMEN
Radiolabeled triiodothyronine (T3) binding to isolated nuclei was measured to compare the binding characteristics of the nuclear receptors in rabbit ventricular and atrial muscle cells. Scatchard analysis of the binding data yielded a maximum binding capacity of 170 +/- 20 fmol per mg DNA and apparent dissociation constant of 525 +/- 100 pM for ventricular nuclei. The binding capacity and the dissociation constant for the atrial muscle cell nuclei were 55 +/- 10 fmol per mg DNA and 500 +/- 75 pM, respectively. The results suggest that the binding capacity for T3 receptor in the atrium is considerably lower than that found in the ventricle. The reduced binding capacity of the T3 receptor in the atrium might reflect differences in the nuclear T3 receptors between ventricle and atrium.
