Enzymes in mitochondria

Superoxide dismutase (SOD) enzymes are metallopro-teins that detoxify superoxide anions (02) by converting them to H202, which is subsequently reduced to water. SOD enzymes include the manganese (Mn) enzyme in mitochondria (SOD2) and the Cu/Zn... 

Robinson, J.B. Srere, P.A. (1985). Organization of Krebs tricarboxylic acid cycle enzymes in mitochondria. J. Biol. Chem. 260, 10800-10805. 

When Murad, Furchgott, and Ignarro received their Nobel Prizes, however, scientists still did not know exactly how nitroglycerin was broken down by the body and converted into nitric oxide. In 2002, researchers at Duke University in North Carolina found an enzyme in mitochondria, the cell s powerhouse, that they believe is responsible for this process. This discovery also explained a phenomenon that doctors had long observed—over time, nitroglycerin stops working and no longer relieves the patient s chest pain. 

Oxidation of fatty acids consumes a precious fuel, and it is regulated so as to occur only when the need for energy requires it. In the liver, fatty acyl-CoA formed in the cytosol has two major pathways open to it (1) J3 oxidation by enzymes in mitochondria or (2) conversion into triacylglycerols and phospholipids by enzymes in the cytosol. The pathway taken depends on the rate of... 

Most of the enzymes in mitochondria are imported from the cytoplasm the enzyme proteins are largely coded for by nuclear DNA (Chap. 17). The enzymes are disposed in various specific regions of the mitochondria (Table 1.2) this has an important bearing on the direction of certain metabolic processes. 

In plants, some steps of the biosynthesis of tetrahy-drofolate, biotin, and lipoate proceed in mitochondria (7, 15), whereas the biosynthesis of vitamin B2 is operative in plastids (67). In apicomplexan protozoa, enzymes in mitochondria, in the apicoplast (an organelle that is believed to have a common evolutionary origin with chloroplasts) and in the cytoplasmic... 

The Krebs cycle is a series of reactions catalyzed by sev en enzymes in mitochondria. Its function is to catalyze removal of electrons from nutrients and to transfer them to NAD and FAD, producing NADH plus H, and FADHj, respectively. These reduced cofactors exist only momentarily in their reduced (err oxidized) forms as they continually accept and then donate electrons to the respiratory chain. The respiratory chain, composed of a number of cytochromes, uses electrons for reduction of to water, This reduction process is accompanied by or coupled with the regeneration of ATP, that is, conversion of A DP back to ATE The overall effect may be summarized thus The Krebs cycle and respiratory chain arc used for oxidizing nutrients io COy and for the production of energy. 

ATP synthase An enzyme in mitochondria that produces ATP by adding a phosphate group to the molecule ADP. 

Proportion of enzyme in wall protein Proportion of enzyme in cytosol Proportion of enzyme in mitochondria... 

Fig. 2. Model of the functional and physical organization of P-oxidation enzymes in mitochondria. (A) P-Oxidation system active with long-chain (LC) acyl-CoAs (B) P-oxidation system active with medium-chain (MC) and short-chain (SC) acyl-CoAs. Abbreviations T, camitineiacylcamitine translocase CPT 11, carnitine palmitoyltransferase 11 AD, acyl-CoA dehydrogenase EH, enoyl-CoA hydratase HD, t-3-hydroxyacyl-CoA dehydrogenase KT, 3-ketoacyl-CoA thiolase VLC, very-long-chain.

More recently Huang and Cavalieri (1979) have studied a similar enzyme in mitochondria isolated from spinach leaves. This enzyme had a pH optimum at 8.0-8.5 with a A , for proline of 28 mAf. The enzyme was linked to the mitochondrial electron transport system and MgCl2 and flavin adenine dinucleotide were required for maximal activity. The spinach oxidase also was inactive after Triton X-100 treatment. 

The exposure, on the bacterial plasma membrane, of so many enzymes that, in the host, are well protected behind mitochondrial membranes, makes bacteria particularly susceptible to selectively toxic agents. The case of oxine, and other chelating drugs that act similarly, was discussed in Section 2.3. For the distribution of enzymes in mitochondria see Table 4.5. 

Enzymological studies on phospholipid-synthesizing enzymes in plants have turned up no m or differences from analogous enzymes in animals and microorganisms. The subcellular location of the enzymes in mitochondria and the ER is also similar to the situation in animal tissue. The enzymes associated with the chloroplast are of particular interest, both in the synthesis of LPA and PA. Further studies on the chloroplast should reveal important aspects of the phospholipid economy, such as the origin of the phospholipids of the chloroplast envelope and the origin of PG in the lamellae. 

A hydrogen cyanide concentration of 300 mg/m in air will kill a human within about 10 minutes. It is estimated that hydrogen cyanide at a concentration of 3500 ppm (about 3200 mg/m ) will kill a human in about 1 minute. The toxicity is caused by the cyanide ion, which halts cellular respiration by inhibiting an enzyme in mitochondria called cytochrome c oxidase. 

The use of biocatalysis for synthetic chemistry is significantly important for reducing the environmental footprint of chentical processes. The possibility of setting up a cascade of enzyme-catalyzed reactions in the same pot is very attractive. In nature, many biochemical transformations are achieved through a combination of several different proteins [65]. For example, the enzymes in mitochondria were settled on the surface of a compartment, in its interior, in its membrane or in any combination of these for the citric acid-catalyzed cycle. Van Dongen et al. mimicked this method to design one porous polymersome to anchor enzymes at three different locations in their lumen (glucose oxidase, GO ), in their bilayer membrane Candida antarctica lipase B, CalB), and on their surface (horseradish peroxidase, HRP). As shown in Scheme 8.22, a mixture of block... 

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