The Activity of a Deaminase


Diagnostic Microbiology In Action
  Principles of Diagnostic Microbiology
    Primary Media for Isolation of Microorganisms
    Some Metabolic Activities of Bacteria
      Simple Carbohydrate Fermentations
      Starch Hydrolysis
      Production of Indole and Hydrogen Sulfide, and Motility
    Activities of Bacterial Enzymes
      The Activity of Urease
      The Activity of Catalase
      The Activity of Gelatinase
      The Activity of Deoxyribonuclease (Dnase)
      The Activity of a Deaminase
    Principles of Antigen Detection and Nucleic Acid Assays for Detection Identification of Microorganisms
      Antigen Detection Assays
      Enzyme Immunoassay (Eia)
      Nucleic Acid Detection Assays

Most bacteria possess a battery of enzymes that specifically break down individual amino acids. In the process, the amine group on the molecule is removed and the amino acid is degraded, the reaction being known as deamination. The deaminases that effect this type of change are named for the particular amino acid substrate for which they are specific. In this experiment, we will see the effects of a phenylalanine deaminase (PDase) produced by some bacteria.

When the amino acid phenylalanine is incorporated into a culture medium in which PDase-producing bacteria are growing, the substrate is degraded to phenylpyruvic acid. The reaction is made visible by adding ferric ions, which react with the newly produced acid to form a green compound. The appearance of a green color in a medium that was colorless when inoculated is evidence of the activity of the deaminase (see colorplate 22).

Purpose To observe the activity of PDase and to distinguish bacteria that produce it from those
that do not
Materials Slants of phenylalanine agar
Dropping bottle containing 10% ferric chloride
Slant cultures of Escherichia coli and Providencia stuartii

  1. Inoculate each of the two cultures on a separate slant of phenylalanine agar.
  2. Incubate the new cultures at 35°C for 24 hours.
  3. Examine the tubes for heavy growth. If it is adequate, run a few drops of 10% ferric chloride solution down the surface of each slant.
  4. Observe the tubes for development of a green color.