Cytochrome succinylation

Early isotope tracer experiments by David Shemin permitted the elucidation of the formation of the immediate precursor of the porphyrin needed for the cytochromes and for hemoglobin. These studies indicated that the glycine methylene carbon and nitrogen were incorporated along with both carbons of acetate. Subsequent enzymatic studies in both bacteria and animals revealed a condensation reaction between succinyl-CoA and glycine to yield 5-amino-levulinate and C02 (presumably by way of an enzyme-bound /3-keto acid, a-amino-/3-ketoadipate) (fig. 22.13). 

Fig. 20.1. Generalized scheme of the main pathways of aerobic and anaerobic carbohydrate degradation in parasitic flatworms. The aerobic pathway is indicated by open arrows, whereas the anaerobic pathway (malate dismutation) is indicated by solid arrows. Abbreviations AcCoA, acetyl-CoA ASCT, acetateisuccinate CoA-transferase C, cytochrome c CI-CIV, complexes I—IV of the respiratory chain CITR, citrate FRD, fumarate reductase FUM, fumarate MAL, malate Methylmal-CoA, methylmalonyl-CoA OXAC, oxaloacetate PEP, phosphoenolpyruvate PROP, propionate Prop-CoA, propionyl-CoA PYR, pyruvate RQ, rhodoquinone SDH, succinate dehydrogenase SUCC, succinate Succ CoA, succinyl CoA UQ, ubiquinone.

Fig. 5.2. Possible metabolic pathways in facultative anaerobic mitochondria. Shaded boxes show components of the electron-transport chain used during hypoxia, open boxes are components used during aerobiosis, and the hatched boxes (complex I and ATP-synthase) are components used under aerobic as well as anaerobic conditions. ASCT acetate succinate CoA-transferase, C cytochrome c, Cl, CIII and CIV complexes I, III and IV of the respiratory chain, CITR citrate, ECR enoyl-CoA reductase (such as present in Ascaris suum), ETF electron-transfer flavoprotein, ETF RQ OR electron-transfer flavoproteimrhodoquinone oxidoreductase, FRD fumarate reductase, FUM fumarate, MAE malate, OXAC oxaloacetate, PYR pyruvate, RQ rhodoquinone, SDH succinate dehydrogenase, SUCC succinate, Succ-CoA succinyl-CoA, TER trans-2-enoyl-CoA reductase (such as present in E. gracilis), UQ ubiquinone...

If you need more haemoglobin for tomorrow—for tomorrow And your cytochromic store s run out of steam—out of steam There s a metabolic pathway you should follow—you should follow Biosynthetic route that leads to haem—leads to haem In mitochondrion the path commences—path commences The d-amino laevulinate way— inate way Glycine decarboxylates when it condenses—it condenses On the synthetase with succinyl Co A. 

Heme, one of the most complex molecules synthesized by mammalian cells, has an iron-containing porphyrin ring. As described previously, heme is an essential structural component of hemoglobin, myoglobin, and the cytochromes. Almost all aerobic cells synthesize heme because it is required for the cytochromes of the mitochondrial ETC. The heme biosynthetic pathway is especially prominent in liver, bone marrow, and intestine cells and in reticulocytes (the nucleus-containing precursor cells of red blood cells). Heme is synthesized from the relatively simple components glycine and succinyl-CoA. 

Heme Glycine and succinyl CoA Liver, bone marrow Heme from liver is incorporated into cytochromes. Heme from bone marrow is incorporated into hemoglobin. 

Low et al. (2004) have proposed a model to explain thioacetamide-induced hepatotox-icity and cirrhosis in rat livers. The pathways of thioacetamide-induced liver fibrosis were found to be initiated by thioacetamide S-oxide derived from the biotransformation of thioacetamide by the microsomal flavin-adenine nucleotide containing monooxygenase and cytochrome P450 systems and involve oxidative stress and depletion of succinyl-CoA, thus affecting heme and iron metabolism. Karabay et al. (2005) observed such hepatic damage in rats with elevation of total nitrite level in livers and decrease in arginase activity. The authors have reported that nitrosative stress was essentially the critical factor in thioacetamide-induced hepatic failure in rats. 

To study the formation of a complex between cytochromes a and c, chemically modified cytochrome c was used in experiments on the cytochrome oxidase activity in place of native cytochrome c. As is known well, about twenty lysine residues are present per molecule of cytochrome c. About 70% of these were acetylated with acetic anhydride (Section II.B.2.a). In other experiments, about 70% of these groups were succinylated with succinic anhydride (Section II.B.2.6). By these procedures, it is generally believed that the e-NHj group of lysine is substituted first, although there is some possibility that in the above treatment not only this group but also the other amino acid residues such as histidine are substituted. 

Since the positively charged groups of cytochrome c are decreased to some extent by these chemical modifications, it seems likely that the affinity of these modified cytochrome c s for cytochrome a would be decreased more after succinylation than after acetylation. Therefore, it was expected that succinylation would have a greater effect on cytochrome oxidase activity, if no alteration other than acylation results from this treatment. Using chemically modified reduced cytochrome c, a study was made of whether cytochrome a was reduced and whether the... 

Fig. 15. Effect of chemically modified cytochrome c on the reduction of cytochrome a. (A) Acetylated cytochrome c. (B) Succinylated cytochrome c. The sample cuvette contained 9.1 x 10" M phosphate buffer at pH 7.4, 1% Emasol 1130, 3.3 X I0 MKCN, 2.5 x I O M cytochrome a, 1.0 x 10 M hydroqui-none, and 4.5 x I0" M cytochrome c or 4.8 x 10 M modified cytochrome c. The total volume was 3.0 ml. The reaction was initiated by the addition of hydro-quinone. The reduction was determined by measuring the increase in optical density of the

Fig. 16. Effect of chemically modified cytochrome c on the cytochrome oxidase activity of cytochrome a. The activity was measured manometrically as described in the previous communication (Yonetani, 1959). Key (A) native cytochrome c (B) 22% succinylated cytochrome c or 32% acetylated cytochrome c.

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