A contractile protein from leucocytes Its extraction and some of its properties

Abstract 1. 1. A contractile protein was isolated from equine leucocytes. The protein exhibited superprecipitation at low ionic strength in presence of Mg 2+ and ATP and possessed ATPase (EC 3.6.1.3) activity. The effect of divalent cations, Mg 2+ and Ca 2+ , on the ATPase activity resembled that on actomyosin from muscle. 2. 2. Electron micrographs of the protein showed, at high ionic strength without ATP, the “arrowhead” structure characteristic of myosin B from striated muscle. Thick and thin filaments were observed at low ionic strength at a relatively high ATP level. 3. 3. The possible role of the protein in the movement of leucocytes is discussed.