Extractability and properties of the contractile proteins of vertebrate smooth muscle

Abstract

The vertebrate smooth muscles differ from the striated ones by their larger extracellular space, the smaller size of their cells and their high content in extracellular components. Furthermore, the smooth muscle cell is a bifunctional biological unit able to carry on also an important biosynthetic activity. The contractile proteins of vertebrate smooth muscle are extractable at low ionic strength contrarily to those of striated muscle. The partition of the salt extractable nitrogen between the low and high ionic strength extracts is very different in these two cases. Acidification of low ionic strength extracts of vertebrate smooth muscle at pH 5 allows precipitation of the contractile proteins quantitatively together with a large amount of contaminants typical of the smooth muscles. Comparison of the contractile proteins of vertebrate smooth muscle with their striated counterparts shows that actin is a very constant component of the contractile machinery, that tropomyosin holds an intermediate position, while myosin is the most variable. The smooth muscle myosin differs not only by some general properties as salting-out range and thermostability, but also by the behaviour of various parts of the molecule. The globular head has a different ATPase activity and is responsible for the very peculiar immunological behaviour of this myosin. The point along the myosin rod which is attacked by trypsin is much more resistant to proteolysis. The light meromyosin is more soluble and differs very much in amino acid composition. The comparative study of myosin reveals only minor variations from one species to the other but more or less wide ones within each species according to the type of muscle examined.

PROPERTIES OF PHYSARUM MYOSIN PURIFIED BY A POTASSIUM IODIDE PROCEDURE

“…Because of its solubility at low ionic strength, Physarum myosin would be most similar to smooth muscle myosin, except that very low or no actin activation has been found with the latter (16). This is probably a minor difference due to problems similar to those encountered with the Physarurn system--namely, i n a d e q u a t e purification, dependence on actin-myoSin ratio, and sensitivity to sulfhydryl oxidation.…”

“…Similar problems exist for other systems including vertebrate smooth muscle myosin (16). Recently, Puszkin and Berl (17) revived the use of potassium iodide (KI) (18,19) to depolymerize and separate brain actin from a myosin component on sucrose density gradients containing A T P and KI.…”

Replication of smooth muscle cells in vascular disease.

“…Myosin from smooth and striated muscle differs not only in amino acid composition (Hamoir, 1973), the type of light chains, and chemical properties of the myosin molecules (Hartshorne and Gorecka, 1980), but, also, in the way the molecules assemble into filaments (Small and Sobieszek, 1980). Cardiac muscle myosin can be found in three isoenzymatic forms which have been designated VI, V2, and V3 (Hoh et al, 1977).…”

Modification of the Mechanical Response of the Smooth Muscles of Pregnant Mouse Myometrium and Guinea Pig Ileum by Cadmium and Manganese Ions

“…This decoupling was seen commonly in either normal, excess K, low Na media or during the application of carbachol. A straightforward interpretation might be that the contractile protein, which possesses also ATPase activity (YAMAGUCHI et al, 1970;HAMOIR, 1973), was impaired by Cd. It has been known that Cd ion is one of potent SH-binding reagents, and that there are two different kinds of SH-groups involved in ATPase activity in myosin and in functioning of actomyosin of the skeletal muscle.…”