Characterization of γ-glutamyltranspeptidases from dormant garlic and onion bulbs

This study investigated the characteristics of γ-glutamyltranspeptidases (GGTs) isolated from dormant garlic (Allium sativum L.) and onion (Allium cepa L. var. agrogatum Don) bulbs. GGTs were isolated using (NH ₄)₂ SO ₄ precipitation and hydrophobic interaction chromatography (phenyl-Sepharose column). The optimal temperature, optimal pH of extraction, and the effects of metal ions and organic compounds on the activity of GGTs were investigated. The optimal pH of the GGTs of garlic and onion was 5 and 7, respectively; the optimal temperatures were 70 and 50°C, respectively. Garlic's GGT had a major band at 53 kDa, whereas onion's GGT had two bands at 55 and 22 kDa. Cu²⁺, Mn²⁺, Fe²⁺, Mg²⁺, glucose, aspartic acid, and cysteine significantly enhanced the activity of garlic's GGT. Lysine and proline remarkably promoted the activity of onion's GGT, whereas Cu²⁺, glucose, and aspartic acid repress its activity. These results may deepen our understanding of allium GGTs and promote the commercial production of bioactive allium compounds.