- The apolipoprotein A-I binding protein of placenta and the SP-40,40 protein of human blood are different proteins which both bind to apolipoprotein A-I. Ehnholm, C., Bozas, S.E., Tenkanen, H., Kirszbaum, L., Metso, J., Murphy, B., Walker, I.D. Biochim. Biophys. Acta (1991)