Catecholamine-beta-alanyl ligase in the medfly Ceratitis capitata

Area of Science:

• Biochemistry
• Insect Physiology
• Enzymology

Background:

• Dopamine (DA) and norepinephrine (NE) derivatives are crucial for insect cuticle sclerotization and pigmentation.
• These catecholamines serve as precursors for cross-linking within the cuticle structure.

Purpose of the Study:

• To investigate the enzymatic conjugation of beta-alanine with DA and NE in the medfly, Ceratitis capitata.
• To characterize the enzyme responsible for these reactions and its substrate specificity.

Main Methods:

• Preparation of protein extracts from medfly prepupae.
• Enzymatic assays to measure the conjugation of beta-alanine with DA and NE.
• Kinetic parameter determination (Vmax, Km) for both substrates.
• Analysis of enzyme behavior under heat inactivation and in the presence of metal ions (Mg2+, Mn2+, Co2+).
• Comparison of enzymatic activity in wild-type and melanic mutant insects (niger and ebony(4)).

Main Results:

• The protein preparation successfully conjugated beta-alanine with DA to form N-beta-alanyldopamine (NBAD) and with NE to form N-beta-alanylnorepinephrine (NBANE).
• The synthesis of NBANE was demonstrated for the first time.
• Kinetic parameters for both DA and NE substrates were determined.
• The same protein exhibited activity towards both DA and NE, showing similar responses to heat, metal ions, and inhibition.
• Melanic mutants defective in NBAD synthesis were also unable to synthesize NBANE.
• The enzyme also acylated tyrosine to produce sarcophagine, but with lower efficiency. Mutant extracts failed to synthesize sarcophagine.

Conclusions:

• The enzyme previously identified as NBAD synthase possesses broad substrate specificity.
• This enzyme is responsible for the synthesis of both NBAD and NBANE, and also sarcophagine.
• We propose renaming this enzyme catecholamine-beta-alanyl ligase.