Effect of reducing agents on proteolytic and keratinolytic activity of enzymes of Microsporum gypseum.

The effect of sodium sulphite, cysteine, glutathione, mercaptoethanol and dithioerythritol (0.1-10 mmol l-1) on the activity of proteases of Microsporum gypseum was studied using azocasein, cross-linked bovine serum albumin and keratin as substrates. With the substrate without disulphide bonds (casein) no stimulation was found, and reducing agents inhibited proteolysis in most cases. With the remaining two substrates, all substances enhanced the activity of proteases probably through the cleavage of the substrate disulphide bonds. Sulphite was more effective than the four used thiols and enhanced the activity against serum albumin up to 3.2 times and against keratin up to 2.9 times. Using sulphitolysed sheep wool, keratinolytic activity increased after sulphitolysis of more than 20% of disulphide bonds. With the fully sulphitolysed wool the activity increased 43 times. The obtained results support the author's hypothesis on keratin degradation by sulphite excretion prior to attack by fungal proteases. Stimulation of proteolysis and keratinolysis by cleavage of disulphide bonds is not specific for dermatophytic proteases because trypsin and pronase behaved similarly in the experiments.