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THE ACTIXOAIYCETES, Vol. I 



lated cultures of streptomyces, only one 

 failed to liquefy gelatin. The liquefying ac- 

 tion of the others was characterized by vary- 

 ing degrees of rapidity. Many of the organ- 

 isms produce a soluble brown pigment in 

 gelatin, which, according to Beijerinck, is 

 in the nature of a quinone that tends to 

 harden the liciuefied portion of the gelatin. 



The (luantitative ability to secrete pro- 

 teolytic enzymes can also be measured by 

 the degree of gelatin liquefaction and of 

 casein hydrolysis. Many species are also able 

 to decompose complex vegetable and animal 

 proteins. Culture filtrates of certain actino- 

 mycetes were found to contain at least two 

 proteolytic enzymes, one capable of digest- 

 ing casein and the other of attacking the 

 proteins of bacterial cells. 



According to Chaloupka, cultures of strep- 

 tomyces cultivated under different condi- 

 tions secrete more protease in an environ- 

 ment with a low concentration of nitrogen 

 than in media rich in nitrogen. A decrease in 

 the concentration of sugars in the mediiun 

 brings about a decrease in the secretion of 

 the enzyme. Secretion of protease depends 

 on the form of nitrogen, and is lowest in a 

 protein medium, higher with lower peptides, 

 and highest in media containing complex 

 peptides and amino acids. Low secretion of 

 the enzyme in protein media is accompanied 

 by vigorous submerged sporulation of strep- 

 tomycetes; high secretion is connected with 

 lysis of the mycelium. Growth of the culture 

 and enzyme production are greatly stimu- 

 lated by potassium ions. 



The proteolytic enzymes of actinomycetes 

 are more resistant to the effect of higher 

 temperatures than are corresponding animal 

 enzymes; the former enzymes are able to 

 withstand heating at 70°C for 80 minutes 

 though at 80°C they are destroyed. Lieske 

 found that the resistance of the enzymes to 

 temperatures is greater than that of the 

 living cells of the organisms, which are killed 

 at ()2 to ()5°C. According to Krassilnikov 



(1938), many cultures are destroyed upon 

 being heated at 40 to 45°C for a long time, 

 but their proteolytic capacity is not affected. 



The proteolytic activities of the various 

 species of actinomycetes are so marked that 

 Waksman (1919) suggested the use of this 

 property for diagnostic purposes. Lieske, 

 however, stated that proteolysis is not a 

 constant property and cannot be used for 

 characterization of the organisms. Krassil- 

 nikov (1938) tested 200 cultures every 8 to 

 12 months for 3 to 5 years. Various forms of 

 gelatin were used for the test. The results 

 were always identical. A strain that dissolved 

 gelatin rapidly when first isolated continued 

 to do so after 1, 2, 3, 4, and 5 years. Strains 

 that failed to liquefy gelatin at first failed 

 to do so after 2 to 5 years' cultivation. The 

 nonpigmented forms were most active. The 

 pigmented forms were least active. 



Proteolysis may occur only at a late stage 

 in the development of the organism. This 

 may be due to the formation of endoen- 

 zymes, which are liberated on the death of 

 the cells, as contrasted with the exoenzyme 

 produced at an early stage of the develop- 

 ment of the mycelium. The diagnostic prop- 

 erties of proteolysis must, therefore, be based 

 upon early observations during the stage of 

 the rapid growth of the organisms. McCon- 

 nell (1950) and Dion (1950) studied the ex- 

 tracellular proteases produced in submerged 

 culture. 



Species of Nocardia, as a rule, possess 

 much weaker proteolytic systems than do 

 Strcptomyces species. Some, like the patho- 

 genic N. asteroides and the saprophytic A'^. 

 ruber and N. viridis, do not liquefy gelatin 

 at all. Some of the yellow species (N. flava) 

 are weak liciuefiers. There are also reports 

 in the literature that pigmented nocardias 

 did not liquefy gelatin. The white {N. alba) 

 forms, however, are able to liquefy gelatin. 



No large scale production of proteolytic 

 enzyme preparations has so far been ob- 

 tained from actinomycetes. Sterile culture 



