Chloroplasts oxidase system

Chlorophyll b occurs as an accessory pigment of the light-harvesting systems in land plants and green algae, and comprises one-third (or less) of total chlorophyll. The biosynthesis of chlorophyll b has been an area of active research particularly regarding its compartmentalization in chloroplast membranes, identification of the gene for chlorophyllide a oxidase, and characterization of the enzymes involved. ... 

Polyphenol oxidase occurs within certain mammalian tissues as well as both lower (46,47) and higher (48-55) plants. In mammalian systems, the enzyme as tyrosinase (56) plays a significant role in melanin synthesis. The PPO complex of higher plants consists of a cresolase, a cate-cholase and a laccase. These copper metalloproteins catalyze the one and two electron oxidations of phenols to quinones at the expense of 02. Polyphenol oxidase also occurs in certain fungi where it is involved in the metabolism of certain tree-synthesized phenolic compounds that have been implicated in disease resistance, wound healing, and anti-nutrative modification of plant proteins to discourage herbivory (53,55). This protocol presents the Triton X-114-mediated solubilization of Vida faba chloroplast polyphenol oxidase as performed by Hutcheson and Buchanan (57). 

Chloroplast envelope membranes. The two envelope membranes that surround chloroplasts contain numerous enzyme systems some of which are involved in the formation and reduction of semiquinone radicals. These include quinol oxidase and NADPHiquinone/semiquinone reductases. These reactions are one step in more complex reactions including the biosynthesis of specific plastid membrane constituents and the formation of polyunsaturated fatty adds. Some of these enzymes are also involved in the export of protons to the cytosol, which partially regulates the stromal pH during photosynthesis. 

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