Thermal coagulation of serum proteins. III. The effects of pH and of sulfhydryl reagents on the nature of the coagulum.

In solutions of serum heated at 100” at neutrality, the presence of small amounts of sulfhydryl reagents markedly alters the course of coagulation; iodoacetic acid strongly inhibits the formation of a coagulum, while iodoacetamide, methyl iodoacetate, and p-chloromercuribenzoate accelerate the rate at which a solid gel is obtained (1). The formation of a solid onephase coagulum or gel in a heat-denatured serum protein solution requires a certain minimum protein concentration, and the determination of this “least coagulable concentration” can serve as a measure of the coagulative ability of a serum or protein solution (2). The present paper describes the thermal coagulation of bovine plasma albumin and human serum albumin, showing that in each case two different types of coagula can be produced. The nature of the coagulum, as well as the protein concentration required to form a clot or gel, depends on the pH of the system and is also markedly influenced by exceedingly minute amounts of compounds which can react with sulfhydryl groups.