Tryptophan 2,3-dioxygenase activity in rat skin

Area of Science:

• Biochemistry
• Dermatology
• Enzymology

Background:

• The metabolism of L-tryptophan is crucial for various biological processes.
• Understanding tryptophan metabolism in skin is important for dermatological research.

Purpose of the Study:

• To identify and characterize an enzyme system in rat skin responsible for L-tryptophan conversion.
• To investigate the kinetic properties and regulatory factors of this skin enzyme.

Main Methods:

• Enzyme assays were performed on soluble and insoluble fractions of rat skin.
• Activity was measured using L-tryptophan as a substrate.
• Factors like hematin, ascorbate, catalase, and methylene blue were tested for their effects.
• Kinetic parameters (Km) were determined.
• Enzyme activity was compared between plucked and unplucked skin.
• Developmental changes in enzyme activity were assessed from birth to 12 weeks.

Main Results:

• An enzyme system catalyzing L-tryptophan to L-kynurenine (via L-formylkynurenine) was identified in rat skin.
• Activity was stimulated by hematin, ascorbate, and catalase.
• Highest activity was observed in the dorsal posterior skin, with lower activity in the abdominal region.
• Plucked skin showed significantly reduced enzyme activity compared to unplucked skin.
• The enzyme exhibited high specificity for L-tryptophan (Km = 1 microM) and did not degrade D-tryptophan, 5-hydroxytryptophan, or tryptamine.
• Skin enzyme activity peaked at 6 weeks post-birth and then sharply declined, unlike hepatic enzyme activity.

Conclusions:

• Rat skin possesses a distinct enzyme system for L-tryptophan metabolism.
• The enzyme's activity is influenced by cofactors and anatomical location.
• Skin integrity (plucked vs. unplucked) affects enzyme levels.
• A significant developmental regulation of this enzyme occurs in rat skin, with a notable decline after 6 weeks of age.