Chemical modification of dopamine beta-hydroxylase

Area of Science:

• Biochemistry
• Enzymology
• Neuroscience

Background:

• Dopamine beta-hydroxylase (DBH) is the key enzyme in norepinephrine synthesis.
• Understanding DBH's catalytic mechanism requires identifying critical amino acid residues.

Purpose of the Study:

• To investigate the role of specific amino acid side-chains in dopamine beta-hydroxylase activity.
• To elucidate the contribution of histidine, lysine, tyrosine, and methionine residues to enzyme function.

Main Methods:

• Chemical modification of purified dopamine beta-hydroxylase using reagents like diazonium tetrazole and iodoacetamide.
• Titration with 2-chloromercuri-4-nitrophenol to assess free cysteine residues.
• Quantification of modified amino acid residues and correlation with enzyme activity loss.

Main Results:

• No free cysteine residues were detected, precluding sulfhydryl reagent studies.
• Diazonium tetrazole inactivated the enzyme, modifying lysine and tyrosine.
• Iodoacetamide and diethylpyrocarbonate inactivated the enzyme, with significant modification of histidine residues.

Conclusions:

• Histidine residues are essential for the catalytic activity of dopamine beta-hydroxylase.
• The findings implicate histidine in the enzyme's active site and catalytic mechanism.