The isolation and characterisation of guinea-pig polymorphonuclear leucocyte actin and myosin

The contractile proteins actin and myosin have been isolated from the soluble phase of guinea-pig polymorphonuclear leucocytes and partially characterised. Two forms of actin have been identified, designated 'Mg-actin' and 'KCl-actin'. They have different polymerising properties but their propensity to form synthetic homologous and heterologous actomyosins and to inhibit DNAase-1 does not significantly differ. Both show beta and gamma isoelectric forms in focusing gels and the Mg-actin accounts for about 5% of the soluble-phase protein and te KCl-actin around 2%. Leucocyte myosin has been isolated by affinity chromatography on N6-ADP-Sepharose with a good enrichment of both Ca2+-ATPase and the ATPase activity measured in the absence of Ca2+ or Mg2+ and in the presence of EDTA. This protein, too, has the capacity to form synthetic homologous and hybrid actomyosins with enhancement of the basal Mg2+-ATPase activity. The ratio of actin to myosin in the leucocyte calculated on a molar basis is well in excess of 100, a figure consistent with the findings from other non-muscle cells.