Biology 250. Protein Catabolism

General reaction: An enzyme converts a substrate into a product.

Gelatin hydrolysis:

Enzyme: gelatinase

Substrate: gelative (a protein)

Product(s): amino acids

Test results: chilled gelatin gels (negative reaction); chilled amino acids don't (positive reaction)

Urea hydrolysis:

Enzyme: urease

Substrate: urea

Products: ammonia and carbon dioxide

Test results: urea + phenol red turns yellow (negative reaction); ammonia + phenol red turns hot pink (positive reaction)

Indole production from tryptophane (in tryptone broth):

Enzyme: tryptophanase

Substrate: tryptophane

Products: indole ring-containing chemical, pyruvic acid, ammonia

Test results: tryptophane + Kovac's reagent turns yellow (negative reaction); indole ring-containing chemical + Kovac's turns red (positive reaction)

Phenylalanine deamination:

Enzyme: phenylalanine deaminase

Substrate: phenylalanine

Products: phenylpyruvic acid + ammonia

Test results: phenylalanine + ferric chloride, slant surface remains uncolored; phenylpyruvic acid + ferric chloride, slant surface turns green

Hydrogen sulfide production (in motility sulfide medium):

Enzyme: cysteine desulfhydrase

Substrate: cysteine

Products: hydrogen sulfide, ammonia, pyruvic acid

Test results: cysteine + ferrous sulfate (in medium) remains uncolored; hydrogen sulfide + ferrous sulfate (in medium) produces black precipitate in the medium (ferrous sulfide)

Observation of motility (in motility sulfide medium):

Cloudiness (turbidity) throughout medium or moving away from the line made by the stab into the agar indicates that the organism is motile.

Growth only along the line of the stab indicates that the organism is nonmotile.