Localization within chloroplasts of protoporphyrinogen oxidase, the target enzyme for diphenylether-like herbicides.
نویسندگان
چکیده
Plant protoporphyrinogen oxidase is of particular interest since it is the last enzyme of the common branch for chlorophyll and heme biosynthetic pathways. In addition, it is the target enzyme for diphenyl ether-type herbicides, such as acifluorfen. Two distinct methods were used to investigate the localization of this enzyme within Percoll-purified spinach chloroplasts. We first assayed the enzymatic activity by spectrofluorimetry and we analyzed the specific binding of the herbicide acifluorfen, using highly purified chloroplast fractions. The results obtained give clear evidence that chloroplast protoporphyrinogen oxidase activity is membrane-bound and is associated with both chloroplast membranes, i.e. envelope and thylakoids. Protoporphyrinogen oxidase specific activity was 7-8 times higher in envelope membranes than in thylakoids, in good agreement with the number of [3H]acifluorfen binding sites in each membrane system: 21 and 3 pmol/mg protein, respectively, in envelope membranes and thylakoids. On a total activity basis, 25% of protoporphyrinogen oxidase activity were associated with envelope membranes. The presence of protoporphyrinogen oxidase in chloroplast envelope membranes provides further evidence for a role of this membrane system in chlorophyll biosynthesis. In contrast, the physiological significance of the enzyme associated with thylakoids is still unknown, but it is possible that thylakoid protoporphyrinogen oxidase could be involved in heme biosynthesis.
منابع مشابه
Purification and properties of protoporphyrinogen oxidase from the yeast Saccharomyces cerevisiae. Mitochondrial location and evidence for a precursor form of the protein.
Protoporphyrinogen oxidase, the molecular target of diphenylether-type herbicides, was purified to homogeneity from yeast mitochondrial membranes and found to be a 55-kDa polypeptide with a pI of 8.5 and a specific activity of 40,000 nmol of protoporphyrin/h/mg of protein at 30 degrees C. The Michaelis constant (Km) for protoporphyrinogen IX was 0.1 microM. Due to the high affinity of the enzym...
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ورودعنوان ژورنال:
- The Journal of biological chemistry
دوره 267 7 شماره
صفحات -
تاریخ انتشار 1992