Which enzyme is tested for in phenylalanine slants?

Phenylalanine slants are utilized in microbiology to test for the presence of the enzyme phenylalanine deaminase. This enzyme catalyzes the removal of an amino group from phenylalanine, resulting in the production of phenylpyruvic acid and ammonia. The test serves as an important metabolic indicator, particularly in the identification of certain bacteria, such as Proteus, Morganella, and Providencia species, which are known to possess this enzyme.

When phenylalanine is subjected to deamination by the action of the enzyme, the resulting phenylpyruvic acid can be detected by adding a ferric chloride reagent to the culture after incubation. A positive reaction is indicated by the development of a green color, confirming the presence of phenylalanine deaminase.

Other enzymes listed, such as caseinase, lactase, and amino acid decarboxylase, do not relate directly to the reactions occurring in phenylalanine slants and would not yield the specific results associated with the testing of phenylalanine deaminase. Thus, the option indicating deaminase is the correct choice.