[Partial characterization of 2 extracellular aminopeptidases (arylamidases) from the dermatophyte Keratinomyces ajelloi]

Optimization of an extracellular protease of Chrysosporium keratinophilum and its potential in bioremediation of keratinic wastes

Chrysosporium keratinophilum IMI 338142 isolated from a waste site containing organopollutants was studied for its ability to produce extracellular proteases on glucose-gelatin medium. Fungus was observed to be a potent producer of such enzymes. Enzyme secretion was best at 15 days of incubation period at pH 8 and temperature 40 degrees C. Asparagine was repressive to protease expression. No relationship existed between the enzyme yield and increase in biomass. Exogenous sugars suppressed enzyme production in the descending order as follows: glucose > arabinose > maltose > mannose > fructose. The enzyme released showed the ability to decompose two keratin substrates tested. Buffalo skin was the most actively degraded substrate when exogenous glucose was absent. Presence of glucose suppressed both enzyme production and degradation of keratin. However, the rate of keratin degradation was independent of enzyme production.

Exocellular proteases of Malbranchea gypsea and their role in keratin deterioration

Malbranchea gypsea IMI 338,168 isolated from the soils of Keoladeo National Park, Bharatpur was studied for its ability to produce exocellular proteases on glucose-gelatin medium at pH 7; 28 degrees C. The fungus was observed to be a potent producer of such enzymes. Protease production was optimal at 15 days of incubation. Asparagine was repressive to protease expression. No relationship existed between the amount of enzyme production and increase in biomass. Exogenous sugars suppressed enzyme production in descending order as follows: glucose > mannose > maltose > arabinose > fructose. The enzymes expressed showed the ability to degrade three keratinous substrates tested. Buffalo skin was the most actively degraded substrate when exogenous glucose was present, and was also the most resistant to degradation in the absence of glucose. The rate of keratin deterioration was independent of enzyme activity. Production of protease enzymes especially keratinases is ecologically important in a place like a National Park because such enzymes degrade keratinous detritus derived from mammals and birds. Accumulation of such materials can be a cause of pollution and can provide a breeding spot for various types of pathogens.

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.

Preliminary characterization of extracellular proteolytic enzymes of dermatophytes by chromogenic substrates

Thirty-eight chromogenic substrates were used to study the specificity of the proteolytic enzymes of seven species of dermatophytes and three related keratinolytic soil fungi. The source of enzymes were cultivation fluids from cultures of the fungi grown on human hair. The overall specificity of the enzymes of all the keratinolytic fungi was very similar. Aminoacyl- and dipeptidyl-4-nitroanilides, substrates of aminopeptidases and dipeptidyl aminopeptidases respectively, were poor substrates compared to aminoterminally blocked oligopeptidyl derivatives. Of the latter, the best substrates were those with phenylalanine, leucine, alanine, methionine or arginine (i.e. amino acids with hydrophobic or basic side chains) in the P1 position. Of the amino acids in the P2 position, proline was the most effective at accelerating the hydrolysis of the respective substrates. Positions P3 and P4 and even the aminoterminal protecting group were also of importance. The specificity profiles of the proteolytic enzymes corresponded best to those of some well characterized serine proteinases (chymotrypsin, elastase).