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At least 19 recordsLinked to original sources

PubMed1979

Tetrahymena tubulins and in vitro translation of Tetrahymena RNA.

Tetrahymena outer doublet tubulin was compared with neurotubulin and Chlamydomonas flagellar tubulin on SDS-polyacrylamide gels. Tetrahymena alpha tubulin did not comigrate with either brain or flagellar alpha tubulins, although brain, flagellar, and ciliary beta tubulins all comigrated. Axonemal tubulin from Tetrahymena strain ST was compared with this tubulin from strains W, S, HSM, and E, and all were found to have the same mobilities. Poly-A containing RNA was separated from whole cell Tetrahymena RNA by oligo-dT cellulose chromatography. Poly-A+ RNA from 24-h cultures (early exponential growth) stimulated greater incorporation of amino acids into polypeptides in the wheat germ cell-free translation system than did poly-A+ RNA from 36-h and 49-h cultures. When separated on SDS-polyacrylamide gels, the translation products of the 24-h poly-A+ RNA had 2 prominent protein bands which comigrated with alpha and beta tubulin isolated from Tetrahymena cilia. These bands were not found in the translation products of poly-A+ RNA isolated from 49-h cultures or in the translation products of poly-A- RNA.

Animals↗

PubMed1978

Studies in Tetrahymena membranes substrates for desaturation of fatty acyl chains in Tetrahymena pyriformis microsomes.

[1-14-C]Palmitoyl-Co A was incubated with Tetrahymena microsomes containing the complete enzyme system for desaturation during various time periods. The level of [1-14C]palmitoleoyl-CoA increased to a maximum during the 1--3 min incubation time, while [1-14C]palmitoleic acid in the phospholipid reached a maximum level during 6--7 min incubation time. The radioactivity of [1-14C]palmitoleic acid in free fatty acid and the triglyceride fraction was not significantly observed upon 3 min incubation. Incubation of [1-14C]palmitoyl-CoA with microsomes in the absence of NADH produced [1-14C]palmitoyl lipid without desaturation. Radioactive palmitic acids in the microsomal lipids were not converted to palmitoleic acids after addition of NADH by the complete enzyme system. When microsomes prepared from cells labeled with [1-14C]palmitic acid or [1-14C]stearic acid were incubated alone in the presence of O2 and NADH, no significant increase in [1-14C]palmitoleic acid in the phospholipid was observed, wherease an increase in [1-14C]linoleic acid and gamma-[1-14C]linolenic acid did occur at the expense of [1-14C]oleic acid in the phospholipid. From these results it can be concluded that the enzyme involving desaturation of palmitic acid to palmitoleic acid requires palmitoyl-CoA as the substrate. However, the possibility of oleoyl and linoleoyl phospholipids being substrates in the desaturation of Tetrahymena microsomes was suggested.

Acyl Coenzyme A↗

PubMed1975

Studies on tetrahymena membranes. Modification of surface membrane lipids by replacement of tetrahymanol by exogenous ergosterol in Tetrahymena pyriformis.

Tetrahymena pyriformis WH-14 cells were grown in the medium supplemented with ergosterol (1 mg/100 ml) and the effects of replacement of tetrahymanol by ergosterol upon the lipid composition in the surface membranes (cilia and pellicles) were examined. 1. By scanning and freeze-etch electron microscopy it was suggested that exogenous ergosterol would be inserted into the lipid regions in the surface membranes. Although freeze-etched faces of filipin-treated membranes containing the native tetrahymanol showed a random distribution of 85-a protein particles, the ergosterol-replaced membranes after the same polyene treatment revealed the marked ultrastructural alterations on the fracture faces. 2. The replacement of tetrahymanol in membranes by ergosterol induced a profound alteration in the phospholipid class composition and a marked increase in phosphatidylethanolamine with a compensatory decrease in phosphatidylcholine and 2-aminoethylphosphonolipid. 3. There are significant and quantitative but not qualitative changes in the fatty acid composition of total lipids from the ergosterol-replaced membranes. There are also increases in saturated and decreases in unsaturated fatty acids. Phosphatidylethanolamine acyl chains particularly become more saturated, as compared with two other phospholipids, in ergosterol-replaced pellicles. This increase in saturation is due to an appreciable increase in C14:0, C16:0 and iso-C17:0, and a decrease in C18:1(delta9), C18:2(delta9,12) and C18:3(delta6,9,12). 4. These results suggest that profound alterations in phospholipids as well as in their fatty acyl chains are required to modify the overall membrane lipid composition for the maintenance of proper membrane fluidity. Our data would also support the thesis that polat head groups are involved in the membrane lipid organization and that sterols interact selectively with phospholipid molecules containing the appropriate fatty acyl chain composition in biological membranes.

Acetates↗

PubMed1976

Studies on Tetrahymena membranes. In vivo manipulating of membrane lipids by 1-O-hexadecyl glycerol-feeding in Tetrahymena pyriformis.

1. Tetrahymena pyriformis NT-I cells were grown in the medium supplemented with 1-O-hexadecyl glycerol which is the precursor for alkyl ether-containing phospholipids; choline phosphoglyceride and 2-aminoethylphosphonolipid, and alterations in the plasma membrane and microsome lipid composition were examined. No incorporation of supplemented 1-O-hexadecyl glycerol was seen in ethanolamine phosphoglyceride. 2. The hexadecyl glycerol fed membranes contain more polyunsaturated fatty acids than do the native membranes. However, the level of oleic acid (C 18:1) drops strikingly in the phospholipids of plasma and microsome membranes. 3. The hexadecyl glycerol-feeding induced a remarkable alteration in the polar headgroup composition of plasma membrane, especially a large increase in 2-amino-ethylphosphonolipid with a compensatory decrease in ethanolamine phosphoglyceride of plasma membranes. 4. The fatty acyl chain composition of phospholipids, especially ethanolamine phosphoglyceride, of the hexadecyl glycerol-fed plasma membranes and microsomes was found to be significantly different from that of the native membranes. 5. These results may indicate that marked alterations in polar headgroup as well as fatty acyl chain composition of membranes induced by glyceryl ether-feeding would be required for maintaining proper membrane fluidity.

Animals↗

PubMed1977

Studies on Tetrahymena membranes. Palmitoyl-coenzyme a desaturase, a possible key enzyme for temperature adaptation in Tetrahymena microsomes.

(1) Microsomes from a thermotolerant Tetrahymena NT-1 catalyze the conversion of palmitoyl-CoA to palmitoleate. (2) Palmitoyl-CoA desaturase enzyme requires molecular oxygen and NADH or NADPH as cofactor and its activity is inhibited by cyanide. A pH optimum range 7.0--7.3 is observed. (3) There is a clear break at 30 degrees C and a slight bend around 15 degrees C in the Arrhenius plots of palmitoyl-CoA desaturase activity. (4) After quenching from 39.5 degrees C, at 26 degrees C microsomal membranes show small particle-free areas, when examined by freeze-fracture electron microscopy, indicating the onset of phase separation. Larger smooth areas devoid of membrane-intercalated particles are observed in microsomes at 23 and 15 degrees C. The results support evidence that the thermally induced transition of desaturase enzyme activity in related to the altered membrane properties due to temperature change.

Adaptation, Physiological↗

PubMed1979

Studies on temperature adaptation in Tetrahymena. Positional distribution of fatty acids and species analysis of phosphatidylethanolamine from Tetrahymena pyriformis grown at different temperatures.

Phosphatidylethanolamine of 15 degrees C-grown Tetrahymena pyriformis (NT-I) cells contains more polyunsaturated fatty acids than 39.5 degrees C-grown cells. This increase in unsaturation is due to an increase in linoleic (C18 : 2) and linolenic (C18 : 3) acids, and a decrease in myristic (C14 : 0), palmitic (C16 : 0), palmitoleic (C16 : 1) and heptadecanoic (C17 : 0) acids. Compared with 39.5 degrees C-grown cells, the proportion of palmitic acid (C16 : 0) decreased in the 1-position as does at the 2-position in 15 degrees C-grown cells. On the contrary, there is a significant increase in linoleic (C18 : 2 delta 9, 12) and gamma-linolenic (gamma-C18 : 3) acids in the 1- and 2-positions, respectively. Phosphatidylethanolamine has been subfractionated into seven different diglyceride species. In 15 degrees C cells, the amounts of fractions 2 (1-linolenoyl-2-linoleoyl) and 3 (1-linolenoyl-2-palmitoleoyl, 1-linolenoyl-2-oleoyl) increased while there was a great decrease in subfraction 7 (1-myristoyl-2-palmitoleoyl, 1-palmitoyl-2-palmitoleoyl). Since subfractions 1 and 2 contain over 70% linoleic (C18 : 2) and linolenic (C18 : 3) acids, these fractions might be composed mainly of 1-linolenoyl-2-linolenoyl and 1-linolenoyl-2-linoleoyl molecular species at 15 degrees C. These data support evidence that phosphatidylethanolamine would play a principal role as an acceptor of acyl chains for temperature acclimation.

Adaptation, Physiological↗

PubMed1975

Changes in cyclic AMP-dependent protein dinase activity in Tetrahymena pyriformis during the growth cycle.

An adenosine 3':5'-monophosphate-dependent protein kinase II (ATP:protein phosphotransferase, EC 2.7.1.37) was partially purified from the cytosol fraction of an exponentially growing culture of Tetrahymena pyriformis. Protein kinase II represented approximately 90% of the cytosolic protein kinase activity. The enzyme had a high degree of substrate specificity for calf thymus and Tetrahymena histones as compared to casein, protamine and phosvitin. The enzyme incorporated the terminal phosphate of ATP into serine and threonine residues of all the histone fractions. The apparent Km of the enzyme for adenosine 3':5'-monophosphate (cyclic AMP) was 1-10-minus 8 M. Protein kinase II was also activated by other cyclic nucleotides with apparent Km values in the range 2.k-10-minus 6 M. Ther specific activity of the cyclic AMP-dependent protein kinase of Tetrahymena decreases markedly from initial high values during the transition from the lag to early log phase of growth. This is followed by a shrp increase in the activity of the enzyme as the log phase of growth progresses. The specific activity of the enzyme increases rapidly during the heat-induced synchronization of Tetrahymena cells. The capacity for rapid phosphorylation of multiple classed of organelle-specific phosphoproteins and the level of cyclic AMP were maximal in Tetrahymena during the earliest phase of growth. These results demonstrate that the cell cycle of Tetrahymena may be coordinated by marked variations in the level of cyclic AMP which in turn regulate the cyclic AMP-dependent protein kinase.

Animals↗

PubMed1976

Purification and characterization of the histones associated with the macronucleus of Tetrahymena.

Histone fractions have been isolated from the macronucleus of Tetrahymena pyriformis. Five classes of macronuclear histone were purified, using a combination of gel exclusion and ion-exchange chromatography, and were examined with respect to their solubility, electrophoretic, chromatographic, and chemical properties. Tetrahymena H4 is very similar to vertebrate H4, except that it exhibits a larger number of acetylated subfractions. In contrast, the other Tetrahymena histones vary more extensively from their calf thymus counterparts. Tetrahymena H3 resembles calf thymus H3 in its solubility properties and is the only macronuclear histone containing cysteine. However, it differs from vertebrate H3 in composition and has a faster electrophoretic mobility on both urea-acrylamide and sodium dodecyl sulfate-acrylamide gel electrophoresis. Tetrahymena H3 also displays a level of acetylation higher than that reported for its vertebrate homologue. Approximately 45% of macronuclear H2B, which resembles calf thymus H2B in composition and solubility, is present in a (mono)acetylated form, not detected in vertebrate somatic H2B. H1, though similar to its calf thymus homologue in solubility, modification (by phosphorylation), and other properties, differs considerably in its content of basic, acidic, and hydrophobic amino acids. Tetrahymena does not contain a histone strictly homologous to H2A. Although macronuclear histone X resembles H2A in chromatographic and some solubility properties more like H2B than H2A. Fraction X is polymorphic in sodium dodecyl sulfate-acrylamide gels, migrating as two distinct molecular forms. While it is possible that one form is H2A-like and the other more H2B-like, the observation that both forms of X behave identically in solubility fractionation schemes makes this unlikely. Fraction X is both phosphorylated and acetylated which, in addition to two molecular forms, results in a characteristic heterogeneous pattern on urea-acrylamide gels. Characterization of the histone complement of this lower eucaryote should contribute to the understanding of the evolution and biological role of these basic proteins. Moreover, this description represents the most extensive analysis to date of the histones associated with an amitotic, genetically active nucleus. It will serve as a reference to which the histones of the morphologically distinct, mitotically dividing, and genetically inactive micronucleus of this organism can be compared.

Amino Acids↗

PubMed1978

Dissociation constant of Tetrahymena tubulin-colchicine complex.

Tetrahymena tubulin has a very low affinity for colchicine. The dissociation rate constant (k-1) and association rate constant(k+1) of Tetrahymena tubulin for colchicine were determined in comparison with those of porcine brain tubulin. The k+1 value of Tetrahymena tubulin was about one-twentieth that of porcine brain tubulin, and k-1 of Tetrahymena tubulin was about 680 times greater than that of brain tubulin. The dissociation constant (k-1/k+1) of Tetrahymena tubulin (2.7 X 10(-3) turned out to be ten thousand times greater than that of brain tubulin. This large Kd value explains well the high colchicine concentration requirement reported to block cell division of cilia regeneration of this protozoan.

Animals↗

PubMed1978

Genome structure of Tetrahymena pyriformis.

Reassociation kinetics of DNA from the macronucleus of the ciliate, Tetrahymena pyriformis GL, has been studied. The genome size determined by the kinetic complexity of DNA was found to be 2.0 X 10(8) base pairs (or 1.2 X 10(11) daltons). About 90% of the macronuclear DNA fragments 200-300 nucleotides in length reassociate at a rate corresponding to single-copy nucleotide sequences, and 7-9% at a rate corresponding to moderate repetitive sequences; 3-4% of such DNA fragments reassociate at C0t practically equal to zero. To investigate the linear distribution of repetitive sequences, DNA fragments of high molecular weight were reassociated and reassociation products were treated with S1-nuclease. DNA double-stranded fragments were then fractionated by size. It has been established that in the Tetrahymena genome long regions containing more than 2000 nucleotides make up about half of the DNA repetitive sequences. Another half of the DNA repetitive sequences (short DNA regions about 200-300 nucleotides long) intersperse with single-copy sequences about 1,000 nucleotides long. Thus, no more than 15% of the Tetrahymena genome is patterned on the principle of interspersing single-copy and short repetitive sequences. Most of the so called "zero time binding" or "foldback" DNA seem to be represented by inverted self-complementary (palindromic) nucleotide sequences. The conclusion has been drawn from the analysis of this fraction isolated preparatively by chromatography. About 75% of the foldback DNA is resistant to S1-nuclease treatment. The S1-nuclease resistance is independent of the original DNA concentration. Heat denaturation and renaturation are reversible and show both hyper- and hypochromic effects. The majority of the inverted sequences are unique and about 20% are repeated tens of times. According to the equilibrium distribution in CsCl density gradients the average nucleotide content of the palindromic fraction does not differ significantly from that of total macronuclear DNA. It was shown that the largest part of this fraction of the Tetrahymena genome are not fragments of ribosomal genes.

Animals↗

PubMed1978

Histone-histone interactions in a lower eukaryote, Tetrahymena thermophila.

The six pairwise interactions of Tetrahymena macronuclear histones H2A (formerly HX), H2B, H3, and H4 have been studied using the techniques of circular dichroism and continuous variation. Parallel experiments have been performed with calf thymus histones as controls, and the 12 possible interspecies pairs have also been examined. The behavior of three of the ciliate histones, H2A, H2B, and H3 is virtually identical with that of their vertebrate counterparts. Tetrahymena H4 exhibits a pattern of interactions identical with that of calf thymus H4, but displays significant quantitative differences in the strength of those interactions. Although we have not entirely eliminated the possibility that these differences may be artifactual, we suggest that they reflect the unique primary structure of Tetrahymena H4. These results extend the pattern of histone-histone interactions defined for plants, animals, and fungi to include the protists as well and imply the strong evolutionary conservatism of this pattern in spite of the electrophoretic and compositional differences which exist between homologous histones of different organisms. In addition, they demonstrate conclusively that histone HX should be redefined as Tetrahymena H2A.

Animals↗

PubMed1979

Presence of calmodulin in Tetrahymena.

Ca-dependent affinity chromatography on phenothiazine-Sepharose 4B has been used to isolate a pure protein from the ciliate Tetrahymena pyriformis. This protein has been identified as calmodulin by demonstrating three of the Ca-dependent activities attributed to calmodulins. Tetrahymena calmodulin also has physicochemical properties similar to those of the previously characterized mammalian, coelenterate, and plant proteins, except for a lower molecular weight (15,000) and slightly different CNBr fragments compared to bovine brain calmodulin. Calmodulin is a constituent of demembranated Tetrahymena cilia from which it can be extracted with the crude dynein fraction. Sucrose density gradient fractionation indicated its presence in fractions containing the 14S dynein ATPase. It is concluded that the essential properties of calmodulin have been highly conserved during much of eukaryotic evolution, and it is suggested that calmodulin plays a role in the control of ciliary motility in Tetrahymena.

Amino Acids↗

PubMed1978

Characterization and in vitro polymerization of Tetrahymena tubulin.

Tetrahymena tubulin was purified from the cell extract using DEAE-Sephadex A-50 ion-exchanger and ammonium sulfate precipitation. About 2.2% of the total protein in the 20,000 X g supernatant was recovered as DEAE-Sephadex-purified tubulin fraction. Applying the temperature-dependent polymerization-depolymerization method to this fraction in the presence of Tetrahymena outer fibers as a seed, almost pure tubulin was obtained. Tetrahymena tubulin dimer showed different behavior on SDS-polyacrylamide gels from porcine brain tubulin, and showed very low affinity for colchicine, amounting to about one-twentieth of the binding to porcine brain tubulin. The tubulin fraction failed to polymerize into microtubules by itself. Addition of a small amount of the ciliary outer fiber fragment induced polymerization as demonstrated by viscometric measurements, but the reconstituted microtubules were very unstable in the absence of glycerol. Microtubule-depolymerizing agents such as Ca2+ ions, low temperature, or colchicine all inhibited in vitro polymerization. Although Tetrahymena tubulin purified by the polymerization-depolymerization method could copolymerize with porcine brain microtubules, the DEAE-Sephadex-purified tubulin fraction suppressed the initial rate of porcine brain microtubule assembly in vitro. There seemed to be no differences between cytoplasmic tubulin and outer fiber tubulin in colchicine binding activity or SDS-gel electrophoretic behavior, or between the fine structure of both reconstituted microtubules observed by electron microscopy.

Animals↗

PubMed1975

Putrescine-insensitive S-adenosyl-L-methionine decarboxylase from Tetrahymena pyriformis.

Extracts of Tetrahymena pyriformis contain a soluble S-adenosyl-L-methionine decarboxylase which, in contrast to the enzyme from most eukaryotic organisms, is not stimulated by putrescine or spermidine. The protozoan adenosylmethionine decarboxylase, unlike the putrescine-insensitive enzyme form Escherichia coli, did not require any metal ions for catalytic activity either. Adenosylmethionine decarboxylase from Tetrahymena resembled the prokaryotic enzyme as far the inhibition by methylglyoxal bis(guanylhydrazone) was concerned, but behaved more like putrescine-activated enzyme in regard to the inhibition by 4-bromo-3-hydroxy benzyl-oxyamine. Adesylmethionine decarboxylase from rat liver, baker's yeast, E. coli and Tetrahymena were strongly inhibited by S-methyladenosylhomocysteamine (decarboxylated adenosylmethionine), the product of the reaction. The function of adenosylmethionine decarboxylase from Tetrahymena like that of the enzymes from other organisms appears to be closely connected to the synthesis of spermidine.

Adenosylmethionine Decarboxylase↗

PubMed1991

Lysosomal enzymes produced by immobilized Tetrahymena thermophila.

The ciliated protozoon Tetrahymena thermophila was immobilized for production of secreted lysosomal enzymes in two ways. Cells entrapped in solid Ca-alginate spheres survived but were unable to grow and multiply. However, when encapsulated in hollow Ca-alginate spheres Tetrahymena multiplied well, reaching 0.9 x 10(7) cells/ml. These immobilized cells secreted large amounts of lysosomal enzymes when the medium was changed daily. This system was transferred to a reactor scale using a conical bubble column reactor for semicontinuous cultivation of the encapsulated cells. Under these conditions alpha-glucosidase, beta-glucosidase, beta-hexosaminidase and acid phosphatase were produced for at least 4 weeks. The hollow spheres were stable for 3 months and contained living and secreting Tetrahymena cells during this time. Immobilized T. thermophila cells can thus serve as a good source for production of commercially interesting enzymes.

Acid Phosphatase↗

PubMed1978

Organization of the 5S RNA genes in macro- and micronuclei of Tetrahymena pyriformis.

The organization of the 5S genes in macro- and micronuclei of Tetrahymena pyriformis was studied using restriction endonucleases. After complete digestion of macronuclear DNA with BamH-I or Hpa I, 5S RNA hybridized to a DNA fragment of approximately 280 base pairs (bp). When macronuclear DNA was only partially digested with these enzymes, hybridization with 32P-5S RNA demonstrated an oligomeric series with a spacing of 280 bp. These results indicate that the 5S genes are tandemly repeated in macronuclei and that the repeating unit is 280 bp (or 180,000 daltons). Since 5S RNA is 120 nucleotides, we conclude that the 5S repeat units contain a 120 bp transcribed region and a 160 bp spacer region. When macronuclear DNA was digested with Eco RI, Bgl I, or Eco RI + Bgl I, 5S RNA hybridized to DNA of molecular weight 3--4 X 10(6), suggesting that these enzymes do not cleave within a 5S repeat. These 3--4 X 10(6) dalton fragments define the maximum size of an average cluster of 5S repeated units. Assuming the size of the 5S repeat to be 0.18 X 10(6) daltons, there are about 15--20 5S repeats per average tanden cluster, and since there are 350 5S-genes per haploid genome, there must be approximately 15--20 tandem arrays. Results obtained using micronuclear DNA suggest that organization of the 5S-genes is very similar in macro- and micronuclei. Macronuclear rRNA genes are extrachromosomal palindromic dimers. In contrast, 5S genes in Tetrahymena were found to be integrated within the genomes of both macro- and micronuclei and not linked to the rRNA genes. Moreover, it is unlikely that they are palindromes; rather they appear to be tandemly repeated in "head-to-tail" linkages. Thus the organization of the 5S genes in Tetrahymena is similar to that of higher eukaryotes.

Animals↗

PubMed1976

Numbers of 5S and tRNA genes in macro- and micronuclei of Tetrahymena pyriformis.

Macronuclei of Tetrahymena pyriformis contain approximately 200 copies of the genes for 25S and 17S ribosomal RNA (rRNA) per haploid genome. Micronuclei, however, contain only a few copies of the rRNA genes per haploid complement. Since macronuclei develop from products of meiosis, fertilization and division of micronuclei, we suggested that the multiple copies of the rRNA genes in macronuclei are generated by amplification of the small number of genes in micronuclei (Yao et al., 1974). This process provides a simple mechanism for maintaining the homogeneity of the repeated rRNA gnes. To test if amplification is a general mechanism operating on all repeated genes in Tetrahymena, we have examined the numbers of 5S RNA and tRNA genes in macro- and micronuclei. 5S RNA was purified by polyacrylamide gel electrophoresis and hybridized to saturation against macro- and micronuclear DNA. Approximately 0.013-0.014% of macronuclear DNA and about 0.009% of micronuclear DNA is complementary to 5S RNA. After correcting for the differences in the DNA sequence complexities between the two nuclei, we calculate that there are 300-350 5S genes per haploid macro- or micronuclear genome. From these data we conclude that there is little or no detectable amplification of the 5S genes in macronuclei relative to micronuclei. Similar studies using tRNA indicate that these genes are also highly repeated in both nuclei; about 800 genes are present per haploid genome. Thus, amplification from a small number of genes can be excluded as the mechanism for generating the repeated copies of the 5S and tRNA genes in Tetrahymena and it is likely that another, as yet unidentified, mechanism operates to maintain the homogeneity of these genes.

Animals↗

PubMed1977

Mitochondrial respiratory chain of Tetrahymena pyriformis: the properties of submitochondrial particles and the soluble b and c type pigments.

Submitochondrial particles isolated from Tetrahymena pyriformis contain essentially the same redox carriers as those present in parental mitochondria: at pH 7.2 and 22 degree C there are two b-type pigments with half-reduction potentials of --0.04 and --0.17 V, a c-type cytochrome with a half reduction potential of 0.215 V, and a two-component cytochrome a2 with Em7.2 of 0.245 and 0.345 V. EPR spectra of the aerobic submitochondrial particles in the absence of substrate show the presence of low spine ferric hemes with g values at 3.4 and 3.0, a high spin ferric heme with g =6, and a g=2.0 signal characteristic of oxidized copper. In the reduced submitochondrial particles signals of various iron-sulfur centers are observed. Cytochrome c553 is lost from mitochondria during preparation of the submitochondrial particles. The partially purified cytochrome c553 is a negatively charged protein at neutral pH with an Em7.2 of 0.25 V which binds to the cytochrome c-depleted Tetrahymena mitochondria in the amount of 0.5 nmol/mg protein with KD of 0.8.10(-6) M. Reduced cytochrome c553 serves as an efficient substrate in the reaction with its own oxidase. The EPR spectrum of the partially purified cytochrome c553 shows the presence of a low spin ferric heme with the dominant resonance signal at g=3.28. A pigment with an alpha absorption maximum at 560 nm can be solubilized from the Tetrahymena cells with butanol. This pigments has a molecular weight of approx. 18 000, and Em7.2 of--0.17 V and exhibits a high spin ferric heme signal at g=6.

Cytochrome c Group↗