[Proteolysis of horse blood serum proteins at various stages of antitoxic sera production by the Diaferm-3 method].

When preparing antitoxic sera by the method "Diaferm-3", it was found that proteolysis of the horse blood serum occurs not only at the fermentation step (pepsin treatment at the enzyme-substrate ratio of 1/10, t 20-23 degrees for an hour at pH 3.3 and for the next hour at pH 4.2), but also at the heat treatment step (45 min at pH 4.3, t 56-58 degrees in the presence of ammonium sulfate at a concentration of 140-145 g/l). At the fermentation step immunoglobulins do not split completely into F(ab')2 fragments, 40% of the antitoxic activity being lost at this step. Some ballast proteins--albumin, fibrinogen, etc.--quickly split up into peptides, while other proteins undergo only limited proteolysis. Structural destabilization of serum proteins during thermodenaturing is favorable for the pepsin action and provides for a complete conversion of immunoglobulins to F(ab')2 and Fab' fragments. At this step about 15% of the antitoxic activity is additionally lost. Thus, proteolysis at the thermodenaturation step is an essential part of the "Diaferm-3" process.