α-Chymotrypsin serves as a sole carbon source, sole nitrogen source, and as sole carbon plus nitrogen source for wild-typeEscherichia coliin a totally defined medium. Hence, a mammalian host forE.colimay supply the necessary carbon and nitrogen nutrients for the microorganism. Growth is most rapid when chymotrypsin is a sole nitrogen source,and least rapid with chymotrypsin as a carbon source. The approximate doubling times forE.coliutilizing chymotrypsin as a nitrogen source, carbon plus nitrogen source, and carbon source are 1.6, 4.6, and 11.3 h, respectively. The activity of the residual enzyme in the culture supernates falls off asymptotically over the course of time, as followed by cleavage of glutaryl-L-phenylalanine-p-nitroanilide. Chymotrypsin hydrolyzes succinyl-L-ala-L-ala-L-ala-p-nitroanilide, the elastase substrate, to some extent. Peptidases do not appear to be secreted that hydrolyze such model substrates as benzoyl-DL-arginine-p-nitroanilide, the tryptic and cathepsin B substrate,L-leucine-p-nitroanilide, the leucine aminopeptidase substrate, orL-lysine-p-nitroanilide, the aminopeptidase B substrate. Growth ofE.coliis generally directly related to the loss of chymotryptic activity in the medium. Hence, autolysis of chymotrypsin, i.e., self-degradation, is an important factor for the availability of degradation products of the enzyme to the bacterium for growth purposes. Accordingly, the degradation of a host protein by autolysis presents an opportunity forE.colito survive during periods of host nutritional crisis by utilization of the degradation peptides that are produced during autolysis.Key words: chymotrypsin,Escherichia coli, growth, nutrition, peptide source.
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