R. S. Norton, G. Bobek, J. O. Ivanov, M. Thomson, E. Fiala-Beer, R. L. Moritz and R. J. Simpson. Purification and characterisation of proteins with cardiac stimulatory and haemolytic activity from the anemone Actinia tenebrosa. Toxicon 28, 29-41, 1990.-Three new proteins with cardiac stimulatory and haemolytic activity, designated tenebrosins-A, -B and -C, have been purified from the Australian sea anemone Actinia tenebrosa. These proteins are basic (pI ≥ 9.4), have mol. wt of about 20,000, and have very similar amino acid compositions and N-terminal amino acid sequences. None of the proteins contains cysteine or cystine residues. On isolated, spontaneously beating guinea pig atria they exhibit at 1-2 nM strong positive inotropic and slight to moderate chronotropic effects. In some cases a transient negative inotropic effect occurs prior to onset of the positive inotropic response. The proteins are also haemolytic, producing 50% haemolysis of guinea pig erythrocytes at concentrations similar to those showing positive inotropic effects.