Oxidation cellular location

Lu W-P, Kelly DP (1988a) Cellular location and partial purification of the thiosulphate-oxidizing enzyme and trithionate hydroxylase from Thiobacillus tepidarius. J Gen Microbiol 134 877-885... 

Describing vitamins E and C as having identical anti-oxidant roles in lipid and aqueous cellular locations respectively is almost certainly an over-simplification since they have been shown to interact synergistically and it may be that at the lipid/aqueous interface, ascorbic acid protects vitamin E, or is involved in its restorative reduction after a successful attack on an oxidising free radical. 

Preliminary studies of the enzymes that catalyze the oxidation of arsenite to arsenate in NT-4, NT-14, NT-26, and BEN-5 have been conducted. To date, only the NT-26 arsenite oxidase (Aro) has been purified and characterized (J. M. Santini and J. M. Macy, personal communication). The optimum buffers, pH, and cellular locations of the respective arsenite-oxidizing enzymes are listed in Table... 

Table 2 Comparisons of Optimum Buffer, pH, and Cellular Location of Arsenite Oxidases from Different Arsenite-Oxidizing Bacteria...

The cellular location (endoplasmic reticulum) reaction stoichiometry is the same, mixed-function oxidation, as for P450,... 

This chapter will focus on the families of enzymes that oxidize PUFA, their cellular location, function and substrate specificity, and introduce the role they and their enzymatic products play in cellular health and pathophysiological conditions. 

A variety of thiokinases probably exist, but only a few of them have been identified. Acetic acid and butyryl thiokinase have been purified from a variety of sources, including yeast, liver, and muscle. These two enzymes differ in their specificity for the substrate. Acetic thiokinase catalyzes only the oxidation of propionic, acetic, and acrylic acids, but butyryl thiokinase activates fatty acids of chain lengths ranging from 4-to 12-carbon units. A third thiokinase was also discovered. It acts on fatty acid chains with 5- to 22-carbon units and is found in the microsomes. This intracellular distribution is in striking contrast with the cellular location of all other enzymes involved in fatty acid oxidation, which are all in mitochondria. The palmityl enzyme, which is active in the presence of ATP and CoA, becomes inactive when incubated in the absence of CoA therefore, it has been proposed that the active form of the enzyme involves the formation of an enzyme-CoA complex. The heart, the skeletal muscle, and the kidney also contain a thiokinase that specifically activates acetoacetic acid. Acetoacetic acid thiokinase is absent in liver this observation is significant in the pathogenesis of ketosis. 

Because the carotenoids favour hydrophobic domains they are generally localised in the membranes and lipoproteins of animal cells. In this location they can influence the oxidation of membrane lipids and prevent the passage of free radicals from one cellular compartment to another. Thus, DNA in the nucleus is protected from intracellularly generated ROS by (at least) the nuclear membrane and from extracellular ROS by a number of membranes. Should ROS reach the nucleus, base oxidation can occur. The base most susceptible to oxidation is guanine, although all other bases can also be affected. The cell has the ability to detect damaged bases, excise them. 

Oxidative stress generally describes a condition in which cellular antioxidant defenses are inadequate to completely detoxify the free radicals being generated, because of excessive production of ROS, loss of antioxidant defenses or, typically, both [23]. This condition may occur locally, as antioxidant defenses may become overwhelmed at certain subcellular locations while remaining intact overall, and selectively with regard to radical species, as antioxidant defenses are radical-specific - for example SOD for superoxide and catalase or glutathione peroxidase for H202. 

In eukaryotes, the cytoplasm, representing slightly more than 50% of the cell volume, is the most important cellular compartment. It is the central reaction space of the cell. This is where many important pathways of the intermediary metabolism take place—e.g., glycolysis, the pentose phosphate pathway, the majority of gluconeogenesis, and fatty acid synthesis. Protein biosynthesis (translation see p. 250) also takes place in the cytoplasm. By contrast, fatty acid degradation, the tricarboxylic acid cycle, and oxidative phosphorylation are located in the mitochondria (see p. 210). 

Mitochondria are also described as being the cell s biochemical powerhouse, since—through oxidative phosphorylation (see p. 112)—they produce the majority of cellular ATP. Pyruvate dehydrogenase (PDH), the tricarboxylic acid cycle, p-oxidation of fatty acids, and parts of the urea cycle are located in the matrix. The respiratory chain, ATP synthesis, and enzymes involved in heme biosynthesis (see p. 192) are associated with the inner membrane. 

---