Enzymes chlorophyllase

The early stages of catabolism correspond to the replacement of Mg by two H atoms under acidic conditions and/or by the action of Mg-dechelatase and the cleavage of the phytol chain by the enzyme chlorophyllase. The still greenish intermediates are pheophytins, chlorophyUides, and pheophorbides with intact tet-rapyrrole rings. - ... 

This is a specihc reaction catalyzed by the endogenous enzyme chlorophyllase (chlorophyll-chlorophyllide-hydrolase) (EC 3.1.1.14) giving rise to chlorophyHides. The basic macrocyclic structure is not modified, so that the chromophore properties are maintained and the color is unaltered. However, phytol (which makes the chlorophyll molecule liposoluble) is lost, resulting in a considerably increased polarity of the product. Pheophytin can also be the substrate of the enzyme chlorophyllase, with the reaction product of de-esterification being pheophorbide. Chemical de-esterification of phytol under acid or alkaline conditions is not a specific reaction, and is usually accompanied by oxidative side reactions [27]. 

In vegetable foods subjected to lactic acid fermentation, activity of the enzyme chlorophyllase is very often favored during the process, and dephytylated chlorophyll derivatives are found [133,138-141]. The degradation mechanism proposed is as follows ... 

Except for the slower demise of chlorophyl1-c, the alteration of chlorophyll-a during senescence and death can be attributed to cellular decompartmentalization and resultant action of cellular acids (Mg-loss) and enzymes (e.g chiorophyllase, phytol loss, 35) The relative amounts of pheophytin-a versus pheophorbide-a resulting from senescence-death has been shown to be species specific and is related to chlorophyllase activity (37). Sediment Trap Samples. The alteration of chlorophyll due to senescence/death phenomena, described above, yield a certain suite of pigments. Such arrays, dominated by pheophytin-a, might be expected to form the precursor complement in sediments deposited in an environment free of consumers. Such is obviously not the case in nature. Since the vast majority (e.g. 95-99%) of primary production serves as fodder in marine food webs (38) we must consider heterotrophic alteration of detrital tetrapyrrole pigments. 

Commercial production of the pigments in England was described by Humphrey (49). Chlorophyll is extracted from dried grass or alfalfa with acetone or chlorinated hydrocarbons. Sufficient water is added, depending on the moisture of the plant material, to aid in penetration of the solvent while avoiding activation of chlorophyllase enzyme. Pheophytin may be acid hydrolyzed before copper ion is added resulting in the formation of water soluble copper chlorophyllin. 

Tsuchiya T, Ohta H, Okawa K, Iwamatsu A, Shimada H, Masuda T, Takamiya K-I (1999) Cloning of Chlorophyllase, the Key Enzyme in Chlorophyll Degradation Finding of a Lipase Motif and the Induction by Methyl Jasmonate. Proc Natl Acad Sci USA 96 15362... 

TSUCHIYA T, OHTA H, OKAWA K, IWAMATSU A, SHIMADA H, MASUDA T and TAKAMiYA K. 1999. Cloning of chlorophyllase, the key enzyme in chlorophyll degradation Finding of a lipase motif and the induction by methyl jasmonate. P Natl Acad Sci 96 15362-15367. 

The phytyl ester at C7 in chlorophyll can be removed enzymically by chlorophyllase to afford phaeophytin, or chemically, without affecting the methoxycarbonyl group at CIO under mild acidic or alkaline conditions in an inert atmosphere. In acidic treatment removal of the magnesium atom occurs, thus the semi-synthesis of... 

Formation of ATP from ADP via the cyclic photophosphorylation system Active immobilized enzyme Investigation of the role of the molecular environment on chlorophyllase functioning during its immobilization Active immobilized enzyme... 

Chlorophyllase (EC 3.1.1.4) a plant carboxyester-ase which catalyses the reversible transformation of chlorophyllides to chlorophyll in the last step of chlorophyll biosynthesis (Chlorophyllide a + phytol chlorophyll + H2O). The pH optimum for the reaction is 6.2. The enzyme is found in all plants, in both the green and nongreen parts such as roots. It is localized in the lipoprotein layer of the thylakoid membrane, which contains all the enzymes and pigments of the photosynthetic apparatus. 

The extent of the reaction converting chlorophylls into pheophytins is directly related with the temperature and the time that the blanching treatment lasts [132]. Blanching at low temperature (65°C-80°C) favors activation of the enzyme chlor-ophyllase, and thus the formation of dephytylated chlorophyll derivatives (chloro-phyllides and pheophorbides). At higher temperatures (around 100°C), the enzyme is partially inactivated, but is favored the parallel reaction of pheophytinization. The extent of chlorophyllide and pheophorbide formation will depend not only on the specific conditions of the technological treatment, but also on the level of chlorophyllase activity in the plant material [133]. 

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