Arterial Tropomyosin and a Relaxing Protein Fraction from Vascular Smooth Muscle

Abstract

A procedure for desensitising natural arterial actomyosin by precipitation at 1=0.22 is described. The desensitised arterial actomyosin superprecipitated in the absence of Ca²⁺ and its Mg²⁺-activated adenosine triphosphatase [EC 3. 6. 1. 3] was increased 7 fold suggesting an inhibitor had been removed. When the soluble protein fraction which had been removed from the natural arterial actomyosin at 1=0.22 was replaced, superprecipitation and the Mg²⁺-activated adenosine triphosphatase activity were inhibited. Skeletal troponin complex was also found to be a potent inhibitor of this desensitised arterial actomyosin, but skeletal and arterial tropomyosin were without effect. Polyacrylamide gel electrophoresis showed that tropomyosin was the chief relaxing protein in the soluble arterial protein fraction, together with a low proportion of protein of a similar electrophoretic mobility to that of skeletal troponin complex. Arterial tropomyosin was functionally and electrophoretically identical to skeletal tropomyosin. It is concluded that a relaxing protein system exists in vascular smooth muscle which functions similarly to that in striated muscle.