Some properties of uterus actomyosin and myofilaments

Abstract

Some properties of the actomyosin-like adenosine triphosphatase of the uterus have already been described (see Needham & Cawkwell, 1956). It was shown that this enzyme splits off only one phosphate group and has a pH-activity curve in 05Mpotassium chloride resembling that of myosin from skeletal muscle. The activity, however, is much lower than that of skeletal-muscle actomyosin; rabbit-and pig-uterus actomyosin (with which most of this work was done) also differ from skeletal muscle actomyosin (which is somewhat inhibited at higher concentrations of potassium chloride) in being less active in media containing 0-1 Mpotassium chloride than in those containing 05Mpotassium chloride. Thus at 280, with Ca2+ ion activation, the values for pmoles of inorganic phosphorus liberated/mg. of nitrogen/min. are about 0-2 and 0-6 in media containing 0.1 and

Proteins of the Uterine Contractile Mechanism

“…Actomyosin. As shown in Table 1, an increased number of precipitations at I 0-27 or 0 3 gave actomyosin preparations with adenosine-triphosphatase activity some 50 % higher than the highest reported by Needham & Williams (1959). The most active preparations had viscosity numbers before and after addition of ATP closely similar to those of skeletal-muscle actomyosin and myosin.…”

“…Measurement of adenosine-triphosphate activity. This was done as described by Needham & Williams (1959), inorganic P being estimated by the method of Weil-Malherbe & Green (1951). Except where otherwise stated, the activating ion was CaS+.…”

“…Tryp8in treatment of myosin. This was carried out as described by Needham & Williams (1959) for actomyosin.…”

“…Work on purified actomyosin from uterus muscle has already been described. Needham & Williams (1959) measured the adenosine triphosphatase activity of actomyosin from this source; it was electrophoretically homogeneous and showed mobility resembling that of skeletal-muscle actomyosin. The present enzymic work was done mainly on preparations after a larger number of precipitations at ionic strength 0-27-0-3, and values for adenosine -triphosphatase activity considerably higher than those previously reported were found.…”

A Study of the Mechanism of Contraction in Vertebrate Smooth Muscle

“…From their cross-sectional appearance it was supposed that they must be ribbon-shaped. However, they were so few in number they could not account for all the myosin known to be present in these muscles (Needham & Williams, 1959). It soon became apparent that the presence or absence of thick filaments in tissue sections depended not only on the method of fixation but also on the pretreatment of the living muscle before fixation (Needham & Shoenberg, 1964) and that the thick filaments seen in a preparation might be due either to aggregation or disaggregation during fixation.…”