Peroxisome localization

The size and enzyme composition of peroxisomes vary considerably in different kinds of cells. However, all peroxisomes contain enzymes that use molecular oxygen to oxidize various substrates, forming hydrogen peroxide (H2O2). Catalase, a peroxisome-localized enzyme, efficiently decomposes H2O2 into H2O. Peroxisomes are most abundant in liver cells, where they constitute about 1 to 2 percent of the cell volume. 

Density gradient fractionation techniques some time ago demonstrated the presence of glutamateiglyoxylate aminotransferase in leaf peroxisomes (Kisaki and Tolbert, 1%9). Similar methods subsequently confirmed the presence of peroxisome-localized serinerpyruvate and aspartate aminotransferases in spinach leaves (Yamazaki and Tolbert, 1970). The same study demonstrated aspartate aminotransferase in both chloroplasts and mitochondria. A microbody location for aspartate aminotransferase was also observed by Cooper and Beevers (1969), who purified castor bean glyoxy-somes on density gradients. 

The second major system is the mammalian Lon protease. Lon is primarily localized in mitochondria, with some data indicating that a Lon variant is transported to peroxisomes. Localization to an organelle such as the mitochondria is cruciaL since the mitochondrial structure is enclosed by a double membrane system, making it impermeable to proteasome which is found throughout the rest of the cell. Mitochondria are a major source of free radical generation, and their macromolecules are highly susceptible to oxidative modification. The Lon protease is the only known system for the direct removal of oxidized proteins in mitochondria. 

The firefly enzyme might have its own problem by the fact that it is localized in vivo (yeast, mammalian, and plant cells as in the firefly lantern) in small vesicular structures called peroxisomes (55). This is due to the presence of a peroxisomal translocation signal located at the C-terminal domain of the molecule. The peroxisomal localization may present an additional membrane barrier for in situ detection of the enzyme, although it offers a particular advantage for studying protein transport or targeting to peroxisomes. Removal of the peroxisomal translocation signal has been shown to provide an alternative system in which the modified firefly luciferase is expressed as a cytoplasmic enzyme like bacterial luciferases. 

Table 6.1, Fig. 6.2b) (Ono et al. 2012). OsPA03, 0sPA04, and OsPAOS have PA back-conversion activity (Ono et al. 2012). Studies on Arabidopsis and rice PAOs suggest that, even in other plants, peroxisome-localized PAOs could be predicted to have back-conversion activity. OsPAOl lacks introns, similar to that of the Arabidopsis AtPAOS. OsPAOl expression is induced by treatment with tetraamine, Spm, or T-Spm. In 7-promoter GPP-transgenic rice plants, the initially... 

NLS, nuclear localization signal PTS, peroxisomal-matrix targeting sequence. 

Mevalonate kinase deficiency. Mevalonate kinase and farnesyl-diphosphate synthase are localized in the peroxisome and are involved in the synthesis of isoprenoids. Mevalonate kinase deficiency causes severe developmental delay, dysmorphic features and early death. Mevalonate deficiency has also been observed in the hyperimmuno-globulinemia-and periodic fever syndrome. 

Angermuller S. Peroxisomal Oxidases Cytochemical Localization and Biological Relevance, G. Fischer Stuttgart, New York, 1989... 

Substrate availability to the cell is affected by the supply of raw materials from the environment. The plasma membranes of cells incorporate special and often specific transport proteins (translocases) or pores that permit the entry of substrates into the cell interior. Furthermore pathways in eukaryotic cells are often compartmentalized within cytoplasmic organelles by intracellular membranes. Thus we find particular pathways associated with the mitochondria, the lysosomes, the peroxisomes, the endoplasmic reticulum for example. Substrate utilization is limited therefore by its localization at the site of need within the cell and a particular substrate will be effectively concentrated within a particular organelle. The existence of membrane transport mechanisms is crucial in substrate delivery to, and availability at, the site of use. 

UbclO is required for the biogenesis of the peroxisome, an oxidative organelle [75]. This E2 plays a role in peroxisomal protein import [76] and is recruited to the peroxisomal membrane through an interaction with a partner protein [77]. Membrane-localized UbclO also seems to be spatially proximal to PexlO, which has a RING-like domain [78]. Whether PexlO is a cognate E3 of UbclO remains to be determined, as does the mechanistic role of ubiquitin conjugation in peroxisome biogenesis. 

Cattley, R.C. Glover, S.E. (1993) Elevated 8-hydroxydeoxyguanosine in hepatic DNA of rats following exposure to peroxisome proliferators relationship to carcinogenesis and nuclear localization. Carcinogenesis, 14, 2495-2499 Cattley, R.C., Conway, J.G Popp, J.A. (1987) Association of persistent proliferation and oxidative injury with hepatocarcinogenicity in female F-344 rats fed di(2-ethylhexyl)-phthalate for 2 years. Cancer Lett., 38, 15-22... 

Polyphenol oxidase (PPO) (EC 1.14.18.1 monophenol monooxygenase [tyrosinase] or EC 1.10.3.2 0-diphenol 02-oxidoreductase) is one of the more important enzymes involved in the formation of black tea polyphenols. The enzyme is a metallo-protein thought to contain a binudear copper active site. The substance PPO is an oligomeric particulate protein thought to be bound to the plant membranes. The bound form of the enzyme is latent and activation is likely to be dependent upon solubilization of the protein (35). PPO is distributed throughout the plant (35) and is localized within in the mitochondria (36), the cholorplasts (37), and the peroxisomes (38). Using antibody techniques, polyphenol oxidase activity has also been localized in the epidermis palisade cells (39). Reviews on the subject of PPO are available (40—42). 

Nguyen, T., Zelechowska, M., Foster, V., Bergmann, H. Verma, D.P.S. (1985). Primary structure of the soybean nodulin-35 gene encoding uricase II localized in the peroxisomes of uninfected cells of nodules. Proceedings of the National Academy of Sciences (USA) 82, 5040-4. 

Keller G. A., Pazirandeh M. and Krisans S. (1986) 3-Hydroxy-3-methylglutaryl coenzyme A reductase localization in rat liver peroxisomes and microsomes of control and cholestyramine-treated animals quantitative biochemical and immunoelectron microscopical analyses. J. Cell Biol. 103, 875-886. 

Cattley RC, Glover SE. 1993. Elevated 8-hydroxydeoxyguanosine in hepatic DNA of rats following exposure to peroxisome proliferators relationship to carcinogenesis and nuclear localization Carcinogenesis 14(12) 2495-2499. 

The significance of catalase in the overall prevention of oxygen-derived free radical damage is difficult to decide with precision because of the doubt about the intracellular localization of the enzyme. If it is indeed only sequestered within peroxisomes its principal, or even only, function may be to catalyse the... 

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