Action de quelques métaux bivalents sur la sensibilité de la sérumalbumine à l'action de la trypsine

Abstract

The addition of ionised salts of certain bivalent metals such as calcium and manganese (and to a lesser degree, cobalt and magnesium) to a solution of serumalbumin at pH 7.9 provokes the immediate formation of metallic complexes of the protein, which are nearly, if not completely, unattacked by trypsin. This property of forming complexes exists regardless of the degree of denaturation of the serumalbumin. But the mechanism which controls the diminution of sensitivity toward trypsin is twofold, and depends on the states of denaturation of the protein. The metal can react directly (with serumalbumin warmed) to form complexes with the serumalbumin which is a substrate less sensitive to trypsin. In other cases (serumalbumin not warmed) the metal plays an indirect role by influencing the equilibrium which exists between two forms of serumalbumin; one only of these forms is attackable by trypsin and the metal displaces the equilibrium towards the other form, for which it possesses a greater affinity. The concentration of manganese necessary to obtain half of the total effect which it can provoke is 10 −2 M for the heated serumalbumin, and 10 −4 M for the non-heated serumalbumin. For calcium, these concentrations are slightly higher. Manganese and calcium are thus powerful regulators of the proteolysis of serumalbumin by trypsin. Ethylenediaminotrtracetic acid (complexone) has its own action in the same sense as that of the metals, and not due to the fact that this compound is a reagent of the metals studied. The action of these substances on the substrate is opposite to that which they have with regard to trypsin. Because of this fact, the protein substrates are not indicated in a study of the behaviour of trypsin in the presence of different metals.