A cytochrome b5 electron transport chain in Tetrahymena

Studies on Tetrahymena microsomal electron transport systems: solubilization of microsomal electron transport enzymes involved in fatty acid desaturation

Tetrahymena microsomes were solubilized with five different detergents and the effect on electron transport enzymes involved in fatty acid desaturation was studied. Cytochrome b560ms and NADPH-cytochrome c reductase were solubilized with a low concentration detergent (0.25%), in the order of sodium deoxycholate greater than Renex 690 greater than Triton X-100 greater than octylglucoside greater than sodium cholate, whereas all of these detergents at the high concentration (1%) could solubilize preferentially both enzymes (70-100%). Increasing the concentration of various detergents from 0.5 to 1.0% did not produce an incremental change in NADH-ferricyanide reductase solubilization. NADH-cytochrome c reductase system, which would be catalyzed by the cooperation action of NADH-ferricyanide and cytochrome b560ms, was relatively inactivated by all detergents. Compared to the other four detergents, octylglucoside has a much higher recovery of stearoyl-CoA desaturase activities in the supernatant. Our study suggests that octylglucoside may be more useful for the isolation in active form of cyanide-sensitive factor (CSF) from Tetrahymena microsomes.

Immunochemical evidence for participation of NADPH-cytochrome c reductase in microsomal fatty acyl-CoA desaturation of Tetrahymena cells lacking in cytochrome P-450

Rabbit antibody was prepared against NADPH-cytochrome c reductase of Tetrahymena microsomes. When examined by the Ouchterlony double diffusion test, anti-NADPH-cytochrome c reductase immunoglobulin formed a single precipitation line with Tetrahymena reductase but not rat liver one. The antibody inhibited the NADPH-cytochrome c reductase activity of Tetrahymena microsomes, but it did not affect either NADH-ferricyanide or NADH-cytochrome c reductase activity of Tetrahymena microsomes. The NADPH-dependent desaturation of stearoyl-CoA in Tetrahymena microsomes was inhibited by anti-reductase immunoglobuline, while the NADH-dependent desaturation was affected by neither anti-reductase nor control immunoglobuline. It was suggested that the temperature associated-alteration of NADPH-cytochrome c reductase activities would be important for regulation of microsomal NADPH-dependent desaturase activities in Tetrahymena which contains no cytochrome P-450.

Oleic acid desaturation in Tetrahymena pyriformis

The desaturation of oleoyl-CoA by a microsomal preparation from Tetrahymena has been studied. Desaturation of oleoyl-CoA required oxygen and NADH, and was inhibited by cyanide. HPLC analysis of fatty acid phenacyl esters, prepared from TLC-purified phospholipid, confirmed that radioactivity appeared in oleate, linoleate and gamma-linolenate. Both the time course of desaturation and the apparent desaturation of 1-palmitoyl-2-[14C]oleoylphosphatidylcholine suggested that phospholipid-bound oleate could be a substrate for desaturation. In the crude microsomal preparation, acylation of oleoyl-CoA to give oleoyl phospholipid was rapid. Therefore, preincubation in the absence of NADH was employed to create [14C]oleoyl phospholipids, and kinetic studies were carried out upon subsequent addition of NADH. When data were plotted in a double reciprocal form, a linear function was observed.