PubMed · 13535611
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K LANG, H LANG. 1958. [The proline oxidase complex].. https://pubmed.ncbi.nlm.nih.gov/13535611/
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The biosynthesis of chlorophyll is a strictly light-dependent multistep process in higher plants. The light-dependent step is catalysed by NADPH:protochlorophyllide oxidoreductase (POR, EC.1.6.99.1), which reduces protochlorophyllide (Pchlide) to chlorophyllide (Chlide). POR is nucleus-encoded and post-translationally imported into plastids. It has been proposed that the import of a POR protein isozyme (PORA) is totally dependent on Pchlide and uses a novel import pathway. This proposal is based on findings that PORA import only occurs in the presence of Pchlide and that the presence of overexpressed precursor of Rubisco small subunit (pSS), a protein which is known to use the general import pathway, does not outcompete PORA import. Another study demonstrated that POR precursor protein (pPOR) can be cross-linked to one of the components in the translocation machinery, Toc75, in the absence of Pchlide, and that its import can be outcompeted by the addition of the pSS. This indicates that pSS and pPOR may use the same translocation mechanism. Thus, POR does not necessarily need Pchlide for import--which is in contrast to earlier observations--and the exact POR import mechanism remains unresolved. Once in the stroma, the POR transit peptide is cleaved off and the mature POR protein is associated to the plastid inner membranes. Formation of the correct membrane-associated, thermolysin-protected assembly is strictly dependent of NADPH. As a final step, the formation of the NADPH-Pchlide-POR complex occurs. When POR accumulates in the membranes of proplastids, an attraction of monogalactosyl diacylglycerol (MGDG) can occur, leading to the formation of prolamellar bodies (PLBs) and the development of etioplasts in darkness.
The heterotrophic nitrifier Paracoccus denitrificans expresses a membrane-associated ammonia monooxygenase. The active enzyme has been solubilized in the detergent dodecyl-beta-D-maltoside and purified by standard chromatographic techniques. This is the first purification of an ammonia monooxygenase. The enzyme consists of two subunits with molecular masses of 38 and 46 kDa. The purified enzyme is a quinol oxidase, is inhibited by light and a variety of chelating agents and is activated by cupric ions. These properties indicate that this enzyme has similarities to a family of enzymes including the ammonia monooxygenase from Nitrosomonas europaea and the particulate methane monooxygenase from Methylococcus capsulatus (Bath).
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