The corticosteroids cortisol, cortisone and corticosterone were tested for their ability to affect the hydrolysis of serum albumin, insulin and oxyhaemoglobin incubated with trypsin, chymotrypsin, papain and pepsin. 2. Corticosteroids stimulated the hydrolysis of albumin and oxyhaemoglobin with trypsin between 10% and 200% and inhibited the hydrolysis of insulin by 15% (steroid/substrate molar ratio, 5:1). 3. The degree of stimulation of proteolysis for a given substrate depended on both the nature of the steroid and the protease. Corticosterone did not increase the activity of papain and pepsin with any of the substrates tested. 4. Corticosterone stimulated (fivefold) the denaturation of oxyhaemoglobin measured spectroscopically in 2.4% (w/v) sodium hydroxide. Small changes in the absorption spectrum of haemoglobin solutions were also noted at pH7.8 without a marked change in the basic properties of haemoglobin. 5. With regard to the action of corticosterone on the activity of trypsin, the lack of stimulation when benzoylarginine amide was used as a substrate, the lowering of the stimulation on prior heat denaturation of haemoglobin and the high temperature coefficient for stimulation suggest that the steroid resulted in improved access of the protease to susceptible bonds of the substrate.
