Properties Of δ-Aminolevulinic Acid Dehydratase From Garlic And Its Relationship To Garlic Greening

Garlic (Allium sativum L.) is a perennial herb of the monocot Allium, which has high nutritional value and many physiological functions, known as "natural health products". China is the world’s largest garlic producer, but greening often occurs during the further production processing, which seriously affects the appearance and quality of the product. It prevents further processing and market development of high value-added garlic, causing enormous economic losses.8-aminolevulinic acid dehydratase catalyzes the asymmetric condensation of two molecules of8-aminolevulinic acid (8-ALA) to form the mono pyrrole porphobilinogen (PBG), which is the precursor of various pyrrole compound. Because the molecular structure of garlic green pigment containing pyrrole ring, therefore, ALAD as the only downstream enzymes of ALA metabolic pathway plays a key role on the generate of garlic green pigment. The experiment by measuring the change of ALAD activity and garlic greening strength on different storage temperatures, studied the relationship between ALAD and garlic greening. ALAD were isolated and purified to study the enzymatic properties and kinetic characteristics. To reveal the mechanism of garlic greening and control the garlic greening, and promote the development of the garlic industry has far-reaching significance. The main results were as follows:1During the same storage period (0-180d), the garlic greening strength and ALAD activity at4℃storage were greater than at room temperature storage, and the garlic greening strength and ALAD activity had consistent trend. It showed that low temperature storage could promote garlic greening and the ALAD activity was closely related with the garlic greening.2ALAD was purified up to14.7times with a recovery of20.9%by the method of ammonium sulfate precipitation, DEAE-SepharoseCL-6B ion exchange chromatography, Sephadex G-200gel filtration chromatography, Phenyl Sepharose CL-4B hydrophobic interaction chromatography. By SDS-PAGE, the subunit of ALAD was55.01KDa.3ALAD optimum pH and temperature was8.5and37℃、Li+、Na+、K+、Ca2+、Mg2+Zn2+、Mn2+can promote ALAD activity and Cu2+、Fe3+、Al3+can inhibit ALAD activity, Ba2+had no significant effect on ALAD activity. D-glucose and D-fructose were the inhibitive factors of ALAD activity. ALAD activity can be suppressed by high concentration of DTT, and the low concentration of DTT can promote the ALAD activity. Kinetic characteristics of ALAD were as follows:the Km was0.56mM and the Vmax was181.8U under the optimum conditions.4The greening experiment proved that Al3+and a high concentration of DTT had a good inhibitory effect on garlic greening.