Shigenobu Umeki

Chronic ethanol administration decreases fatty acyl-CoA desaturase activities in rat liver microsomes

The Δ9‐desaturase system in liver microsome from rats treated chronically with ethanol was studied. Stearoyl‐CoA desaturase activity decreased by 80% and palmitoyl‐CoA desaturase activity was not detectable in microsomes from ethanol‐fed rats, while activities of electron transport components such as NADH‐cytochrome c and NADH‐ferricyanide reductases remained unchanged. However, chronic ethanol administration resulted in an adaptive induction of the activity of NADPH‐cytochrome c reductase and the contents of cytochrome b 5 and P‐450. The activity of the terminal component (cyanide‐sensitive factor; CSF) of the desaturase system was greatly depressed by ethanol treatment. The NADH/NAD ratio in microsomes of ethanol‐fed rats increased over 2‐fold. These results suggest that, during chronic ethanol ingestion, decreased activities of Δ9‐desaturases are due mainly to a decreased content of the terminal component of the desaturase system.

Studies on thermal adaptation of Tetrahymena lipids: Alteration in fatty acid composition and its mechanism in the growth temperature shift-up

Abstract A rise in the growth temperature of Tetrahymena pyriformis strain NT-1 from 15 to 34°C resulted in changes in the fatty acid composition of membrane lipids toward higher saturation after a shift-up. The proportion of palmitate (16:0) increased and γ-linolenate (18:3 (6,9,12)) decreased. Alteration in phospholipid composition was completed by a marked increase in phosphatidylethanolamine, with a compensatory decrease in 2-aminoethylphosphonolipid. However, the level of phosphatidylcholine remained unchanged. The rate of incorporation of [1- 14 C]acetate into saturated fatty acids (myristate, 14:0; palmitate; stearate, 18:0) was maximum at 1 h after a shift, while formation of 14 C-labeled unsaturated fatty acids (palmitoleate, 16:1 (9); linoleate, 18:2 (9,12); γ-linolenate) decreased by about 50%. These findings could be explained by the reduced desaturase activities which were due principally to the decrease in the terminal component, cyanide-sensitive factor (CSF), of the microsomal desaturase system. Furthermore, changes induced by temperature shift-up in activities of microsomal reductases and the content of cytochrome b 5 were observed to behave comparably with changes in activities of desaturases.

Variations in the activity of fatty ACYL-CoA desaturases and electron-transport components in Tetrahymena microsomes with temperature and age of culture

Abstract 1. 1.|Alterations in the fatty acid composition of microsomes were most marked in the exponential phase of both 39.5- or 15°C- grown Tetrahymena pyriformis NT-1. 2. 2.|Activities of palmitoyl-CoA and stearoyl-CoA desaturases were lower in 15°C cells than in 39.5°C cells, while the activity of oleoyl-CoA desaturase was higher in 15°C cells. 3. 3.|Activities of the terminal component of the desaturation system as well as all three desaturases (palmitoyl-CoA, stearoyl-CoA, oleoyl-CoA) were higher in the exponential phase than in the stationary phase for cells grown at both temperatures. 4. 4.|NAD(P)H-cytochrome c reductase activity and cytochrome b 5 content were reduced whereas NADH-ferricyanide reductase activity was increased in the stationary phase at both 39.5 and 15°C.

Effects of sterol manipulation on microsomal desaturase activities in Tetrahymena: With regard to thermal acclimation

There was a great increase in microsomal palmitoyl-CoA desaturase activity of ergosterol-replaced Tetrahymena (ergosterol-cells), which exhibited a pronounced elevation of palmitoleate (16:1 delta 9) in fatty acid composition. At 2 hr after the growth temperature-shift from 34 to 15 degrees C (shift-down), palmitoyl-CoA desaturase activity in ergosterol-cells increased 6-fold compared to that in native cells containing tetrahymanol before the shift-down. These results suggest that, unlike drastic increases of palmitoyl-CoA, stearoyl-CoA and oleoyl-CoA desaturase activities by the shift-down in native cells, ergosterol-cells accomplish an adaptive modification of fatty acid composition by a preferential increase in palmitoyl-CoA desaturase activity, being which is principally due to the increased content of the terminal component (cyanide sensitive factor; CSF) of the desaturase system.

Purification and partial characterization of cytochrome b5 from Tetrahymena pyriformis

Abstract With the use of detergents and successive column chromatographies, Tetrahymena b-type cytochrome was purified from microsomes to a specific content of 36.0 nmol per mg of protein. The purified form showed a single band on SDS-polyacrylamide gel with molecular weight of 22,000. The spectral properties of the reduced b-type cytochrome, the α-peak of which is situated at 560 nm and asymmetric with a shoulder at 556 nm, was different from that of rat liver microsomal cytochrome b 5 . However, it was reducible by NADH in the presence of NADH-cytochrome b 5 reductase purified from rat liver microsomes. The results indicated that the microsomal b-type cytochrome should be designated as cytochrome b 5 of a ciliated protozoan, Tetrahymena pyriformis .

Modulation by dexamethasone of the fatty acyl-CoA desaturase system in Tetrahymena microsomes

Dexamethasone produced an increased activity of stearoyl-CoA desaturase through the enhancement of delta 9-terminal component activity, and a corresponding decrease of oleoyl-CoA desaturase activity via the reduced activity of delta 12-terminal component in Tetrahymena microsomes. However, the content of cytochrome b5 as well as the activities of NAD(P)H-cytochrome c and NADH-ferricyanide reductases showed no significant changes by dexamethasone. Additionally, dexamethasone evoked a 3.5-fold increase of intracellular cyclic AMP content 2 hr after administration. These results suggest that dexamethasone may modulate microsomal fatty acyl-CoA desaturase system in Tetrahymena by increasing intracellular cyclic AMP content.

Suppression by dexamethasone of isoproterenol-mediated changes in fatty acyl-CoA desaturase activity ofTetrahymena microsomes

Preincubation ofTetrahymena pyriformis cells with dexamethasone inhibited the microsomal fatty acyl-CoA desaturase activities of isoproterenol-induced modulation; that is, an increase in Δ9-desaturase activity accompanied by a decrease in Δ12-desaturase activity. Although isoproterenol caused an increase in Δ12-terminal component activity with decreased Δ12-terminal component activity, dexamethasone reduced these isoproterenol-mediated activity changes. In cells treated with dexamethasone prior to isoproterenol administration, stimulation of cyclic AMP accumulation by isoproterenol was inhibited. These results suggest that dexamethasone may repress isoproterenol modulation of the activity of terminal components (cyanide-sensitive factor) in the fatty acyl-CoA desaturase system by reducing the cyclic AMP level.

Modification of microsomal lipid composition and electron transport enzyme activities in isovalerate-supplemented cells of novelTetrahymena ISO

Tetrahymena ISO cells, which have an unusually high level ofiso odd-numbered fatty acids, were grown medium supplemented with various concentrations of isovalerate. There was a marked increase in the total proportion ofiso odd-numbered fatty acids in supplemented whole cells (28.9→70.3%) and microsomes (37.7→84%), with a corresponding decrease in normal fatty acids, although no significant alteration of phospholipid composition was observe during 11 hr isovalerate-supplementation. Microsomal palmitoyl-CoA and stearoyl-CoA desaturase activities in isovalerate-supplemented cells decreased by 45.7% and 30.6% during 11 hr, respectively. NADH-cytochrome c reductase and NADH-ferricyanide reductase activities as well as the content of cytochrome b560ms, which is similar to mammalian microsomal cytochrome b5, were reduced in microsomes from 11 hr-supplemented cells, whereas NADPH-cytochrome c reductase activity was constant. It is suggested that the alteration of the cross-sectional area of lipid molecules in the bilayer, which results from the replacement of normal fatty acids withiso-15∶0 andiso-17∶1, would result in the decline of palmitoyl- and stearoyl-CoA desaturation in the isovalerate-supplemented cells, in order to maintain membrane fluidity at a functional level.