Salmonella typhimurium peptidase active on carnosine

Area of Science:

• Microbiology
• Enzymology
• Molecular Genetics

Background:

• Wild-type Salmonella typhimurium utilizes carnosine (beta-alanyl-L-histidine) as a histidine source.
• Carnosine utilization is impaired in specific mutants deficient in peptidase D, encoded by the pepD gene.

Purpose of the Study:

• To biochemically and genetically characterize the enzyme responsible for carnosine utilization in Salmonella typhimurium.
• To elucidate the role of peptidase D in carnosine metabolism and histidine acquisition.

Main Methods:

• Biochemical assays including enzyme activity coelution, coelectrophoresis, and thermal inactivation.
• Genetic analysis of pepD mutants and their peptide utilization patterns.
• Growth yield experiments to assess histidine source importance.

Main Results:

• Biochemical data strongly support peptidase D's carnosinase activity, showing coelution, coelectrophoresis, and identical inactivation rates with dipeptidase activity.
• Genetic mapping confirms that mutations affecting carnosinase activity reside within the pepD gene.
• Analysis of pepD mutants revealed altered enzyme specificities, impacting peptide utilization.

Conclusions:

• Peptidase D is the primary enzyme responsible for carnosinase activity in Salmonella typhimurium.
• The pepD gene is essential for efficient carnosine utilization as a histidine source.
• Carnosine serves as a major utilizable histidine source in nutrient broth for Salmonella typhimurium.