Limonoate dehydrogenase from Arthrobacter globiformis: the native enzyme and its N-terminal sequence

Area of Science:

• Biochemistry
• Enzymology
• Food Science

Background:

• Bitter limonoids, such as limonin, significantly reduce the quality and market value of commercial citrus juices.
• The natural debittering capacity in citrus fruit is limited due to low levels of key enzymes.

Purpose of the Study:

• To isolate and characterize limonoate dehydrogenase (LDH) from Arthrobacter globiformis for potential application in citrus debittering.
• To evaluate the feasibility of enhancing citrus debittering through genetic engineering.

Main Methods:

• Enzyme isolation using ammonium sulfate fractionation, Cibacron Blue affinity chromatography, and DEAE ion exchange HPLC.
• Determination of native enzyme molecular weight (M(r)) via gel filtration HPLC.
• Analysis of subunit molecular weight (M(r)) and N-terminal sequencing using SDS-PAGE.

Main Results:

• Achieved a 428-fold purification of limonoate dehydrogenase from Arthrobacter globiformis.
• The native enzyme has a molecular weight of 118,000 Da, with individual subunits of 31,000 Da.
• The first 16 amino acid residues of the N-terminus were sequenced.

Conclusions:

• The characterized bacterial limonoate dehydrogenase is a promising candidate for improving citrus debittering.
• Cloning the gene for this enzyme into citrus plants could significantly enhance their natural ability to reduce bitterness.