The reaction of cytochrome oxidase with oxygen in the fission yeast Schizosaccharomyces pombe 972h-. Studies at subzero temperatures and measurement of apparent oxygen affinity

1. Cytochrome alpha 3 in whole-cell suspensions of the fission yeast Schizosaccharomyces pombe reacted in the reduced form with CO to give a photodissociable CO complex with absorption maxima at 429, 543 and 591 nm in CO-liganded reduced-minus-reduced difference spectra. 2. Other CO-bound haemoproteins, cytochromes P-420 and P-450, were not photodissociated under the conditions employed. 3. Measurements of the rates of reassociation of CO with cytochrome alpha 3 after flash photolysis over the temperature range from -101 to -109 degrees C gave a value for Eact. of 28.6 kJ/mol. 4. Between -94 and -106 degrees C, O2 reacted with cytochrome oxidase in intact cells to give an oxygenated intermediate (compound A). 5. At -70 degrees C compound A was converted into a second spectrally distinct intermediate (compound B). 6. Electron transport, indicated by the oxidation of cytochromes alpha + alpha 3 and cytochrome c, did not occur until the temperature was raised to -50 degrees C. 7. At room temperature cytochfome oxidase was oxidized to 50% of its steady-state concentration by 0.35 microM-O2.

The reaction of cytochrome omicron in Escherichia coli with oxygen. Low-temperature kinetic and spectral studies

1. The reactions of cytochrome omicron in intact cells of aerobically grown Escherichia coli with O2 and CO have been studied at low temperature. 2. Flash photolysis of CO-liganded cells in the presence of O2 and at temperatures between -79 and -102 degrees C results in the oxidation of kinetically heterogeneous beta-type cytochromes (including cytochrome omicron), but not of cytochrome d. 3. The reaction of reduced cytochrome omicron with O2 involves O2 binding to give intermediate(s) with spectral characteristics similar to that of the reduced oxidase-CO complex. Observation in the alpha-region suggests that unexplained ligand dissociation accompanies the initial O2 binding. 4. At temperatures below -98 degrees C, an 'end point' in the reaction is reached; further reaction and oxidation of cytochrome omicron occurs on raising the temperature. 5. There is a linear relationship between the rate of formation of the oxygen compound and the O2 concentration up to 0.5 mM. The second-order constant for its formation (k+1) is 0.91 M-1.S-1 at -101 degrees C. The reaction is not readily reversible, the value of k-1 being 1.4 X 10(-5) S-1 and the kd 1.5 X 10(-5) M. 6. The energy of activation for this reaction at low temperatures is 29.9kJ (7.1 kcal)/mol. 7. The reaction with O2 is distinguished from that with CO by the markedly lower velocity and high photolytic reversibility of the latter. 8. Comparisons are drawn between the intermediate(s) in the O2 reaction of cytochrome omicron in E. coli and those identified in other bacteria and in the reaction of cytochrome aa3 with O2.

The influence of growth substrate and capacity for oxidative phosphorylation on respiratory oscillations in synchronous cultures of Escherichia coli K12

Fluctuations in cell volume during exponential growth of Escherichia coli K12 changed the effectiveness of the continuous-flow centrifugation method for preparing synchronous cultures. Rates of oxygen uptake in synchronous cultures were measured using an electrode system open to the atmosphere. In synchronous cultures of both the parental strain and an adenosine triphosphatase-deficient mutant, which was incapable of oxidative phosphorylation, respiration rates doubled during the cell cycle but oscillated with a periodicity of approximately half a cycle. Synchronous cultures of the parental strain growing on glycerol and Casamino acids showed a stepwise pattern of oxygen consumption. Continuous flow centrifugation did not markedly affect the increases in the numbers and respiration rates of cells in syndhronous cultures. Respiratory oscillations also occurred on inoculation of a late-stationary phase culture into fresh medium, although synchronous division was not observed. The possible mechanisms underlying respiratory fluctuations under different growth conditions are discussed.

Fluctuations in buoyant density during the cell cycle of Escherichia coli K12: significance for the preparation of synchronous cultures by age selection

The buoyant densities of Escherichia coli K12 were investigated by isopycnic centrifugation in gradients of colloidal silica (Ludox) and polyvinylpyrrolidone. Bacteria from an exponential culture in a defined medium supplemented with hydrolysed casein banded at densities between 1-060 and 1-115 g ml-1; the mean density was 1-081 g ml-1. At the higher densities, two populations of cells were present: smaller cells were approximately twice as numerous as, and half the modal volume of, the population of larger cells. A homogeneous population of cells of intermediate volume equilibrated in the least dense region of the density band. Synchronous cultures were established by inoculating cells selected from the most or least dense regions of the band into spent growth medium. The results are consistent with a fluctuation between maximal density at cell birth and division, and minimal density near the middle of the cell cycle. In synchronous cultures prepared by continuous-flow age selection, the first division occurred after a period that was significantly shorter than the length of subsequent cell cycles. Cells selected by this procedure were of similar mean density to those in the exponential culture but were more homogeneous with respect to size. The possibility that the smallest (and densest) cells in an exponential culture are retained in the rotor, and are thus excluded from the synchronous culture, is discussed.

Fractionation by differential and zonal centrifugation of spheroplasts prepared from a glucose-repressed fission yeast Schizosaccharomyces pombe 972h-

A method is described for the preparation of spheroplasts in high yield from Schizosaccharomyces pombe, by treating cells grown in the presence of glucose and deoxyglucose with snail digestive enzymes. Gentle disruption of such spheroplasts yielded homogenates, from which marker enzymes for nuclei (NAD pyrophosphorylase) and mitochondria (cytochrome c oxidase activity and spectroscopically-detectable cytochromes a + a3) could be quantitatively sedimented by low-speed centrifugation. In contrast to previous findings with Saccharomyces carlsbergensis, cytochrome c oxidase and another mitochondrial enzyme, succinate dehydrogenase, were completely sedimentable by zonal centrifugation in sucrose gradients in the presence of either 2 mM-MgCl2 or 0-4 mM-EDTA. Mitochondria were apparently smaller and of lower buoyant density in gradients containing EDTA. The bulk of the total units of malate dehydrogenase and NADH; cytochrome c oxidoreductase sedimented with mitochondria, whereas NADPH: cytochrome c oxidoreductase was located in fractions containing no mitochondria. The distributions of mitochondrial enzymes were heterogeneous in populations of mitochondria separated on the basis of size or density. The possible origins of mitochondrial heterogeneity in extracts of S. pombe are discussed with special reference to changes in the enzyme activities of cells during the cell cycle.

Effects of sulphate-limited growth in continuous culture on the electron-transport chain and energy conservation in Escherichia coli K12

Growth of Escherichia coli K12 in a chemostat was limited by sulphate concentrations lower than 300 muM. The synthesis of extracellular polysaccharide and a change in morphology accompanied sulphate-limited growth. Growth yields with respect to the amount of glycerol or oxygen consumed were sixfold and twofold lower respectively under these conditions than when growth was limited by glycerol. Sulphate-limited cells lacked the proton-translocating oxidoreduction segment of the electron-transport chain between NADH and the cytochromes, and particles prepared from these cells lacked the energy-dependent reduction of NAD+ by succinate, DL-alpha-glycerophosphate or D-lactate, suggesting the loss of site-I phosphorylation. Glycerol-limited cells contained cytochrome b556, b562 and o, ubiquinone and low concentrations of menaquinone. Sulphate limitation resulted in the additional synthesis of cytochromes d, a1, b558 and c550; the amount of ubiquinone was decreased and menaquinone was barely detectable. Non-haem iron and acid-labile sulphide concentrations were twofold lower in electron-transport particles prepared from sulphate-limited cells. Recovery of site-I phosphorylation could not be demonstrated after incubating sulphate-limited cells with or without glycerol, in either the absence or presence of added sulphate. The loss of site-I phosphorylation in sulphate-limited cells is discussed with reference to the accompanying alterations in cytochrome composition of such cells. Schemes are proposed for the functional organization of the respiratory chains of E. coli grown under conditions of glycerol or sulphate limitation.

Changes in respiratory activities during the cell-cycle of the fission yeast Schizosaccharomyces pompe 972h--growing in the presence of glycerol

1. The specific activities of cytochrome c oxidase, catalase, succinate dehydrogenase, succinate-cytochrome c oxidoreductase, NADH-cytochrome c oxidoreductase, and NADPH-cytochrome c oxidoreductase in mid-exponential-phase batch cultures of glycerol-grown Schizosaccharomyces pombe indicated that the organisms were catabolite-de-repressed. 2. In cultures growing synchronously in the presence of glycerol as sole carbon source, the respiration rate showed two abrupt increases at about 0.45 and 0.95 of the cell-cycle and remained constant in the periods between successive rises. 3. Catalase, succinate dehydrogenase, NADH-cytochrome c oxidoreductase and acid p-nitrophenyl-phosphatase all showed peak patterns of expression in synchronous cultures. 4. Cytochrome c oxidase and cytochromes a+a(3) both showed step patterns of expression with two rises per cell-cycle. 5. Cytochromes c(548), b(554) and b(560) all followed similar time-courses in step patterns of expression, but these were distinct from, and more complex than, that of cytochromes a+a(3). 6. These results are compared with those previously obtained with glucose-grown cultures, and the part played by catabolite repression in the expression of respiratory activities in the cell-cycle is assessed.

Energy-linked reduction of nicotinamide--adenine dinucleotide in membranes derived from normal and various respiratory-deficient mutant strains of Escherichia coli K12

1. Assay conditions are described for the ATP-dependent, uncoupler-sensitive, energy-linked reduction of NAD(+) by succinate, dl-alpha-glycerophosphate or d-lactate in membranes from aerobically grown Escherichia coli. 2. The reaction may be demonstrated in electron-transport particles (ET particles) from cells grown in glycerol, but not in depleted particles washed in low-ionic-strength buffer, or in ET particles from cells grown in glucose. 3. The latter two classes of particles have low specific activities of ATPase (adenosine triphosphatase), succinate dehydrogenase, dl-alpha-glycerophosphate dehydrogenase and d-lactate dehydrogenase relative to undepleted ET particles from cells grown in glycerol. 4. Reconstitution of energy-linked NAD(+) reduction in particles from cells grown in glucose was done by: (a) addition of the high-speed supernatant fraction from sonicates of the same cells; (b) addition of a protein fraction, precipitated by (NH(4))(2)SO(4) from this supernatant, or (c) addition of an (NH(4))(2)SO(4)-precipitated fraction from the low-ionic-strength wash of particles from cells grown in glycerol. 5. The use of (NH(4))(2)SO(4)-precipitated fractions from ATPase- or succinate dehydrogenase-deficient mutants grown in glycerol in the above reconstitution indicated that failure to demonstrate the reaction in particles from cells grown in glucose was a result of inadequate activities of appropriate dehydrogenases, rather than of ATPase. 6. Energy-linked NAD(+) reduction could be demonstrated in particles from a ubiquinone-deficient mutant only after restoration of NADH oxidase activity by adding ubiquinone-1. 7. The measured rate of the energy-linked reaction in particles from a haem-deficient mutant, however, was not stimulated after the ATP- and haematin-dependent acquisition of functional cytochromes. 8. Results are interpreted as evidence of the ubiquinone-dependent, but cytochrome-independent, nature of the site I region of the respiratory chain in E. coli.

The development of cytochromes during the cell cycle of a glucose-repressed fission yeast, Schizosaccharomyces pombe 972h-

1. Spectrophotometric analysis of intact cells of Schizosaccharomyces pombe, harvested from exponentially growing cultures during the phase of glucose repression, revealed the presence of cytochromes a+a(3), c and at least two species of cytochrome b. 2. An absorption maximum at 554nm at 77 degrees K, previously attributed to cytochrome c(1), has been identified as a b-type cytochrome. 3. CO-difference spectra reveal the presence of cytochromes P-420 and P-450 in addition to cytochrome a(3). 4. The cell cycle was analysed by separation of cells into classes representing successive stages in the cell cycle by isopycnic zonal centrifugation. 5. Cytochromes c(548), b(554) and b(560) each exhibited a single broad maximum of synthesis during the cell cycle. 6. Amounts of cytochromes a+a(3) and b(563) (tentatively identified as cytochrome b(T) by its reaction on pulsing anaerobic cell suspensions with O(2)) oscillated in phase, and showed two maxima during the cycle; the second maximum of cytochromes a+a(3) was coincident with a maximum of activity of enzymically active cytochrome c oxidase. 7. The amount of cytochrome P-420 decreased during the first three-quarters of the cell-cycle, whereas that of cytochrome P-450 increased during this period. 8. The discrepancy between spectrophotometric and enzymic assay of cytochrome c oxidase, the changing ratio of cytochrome a(3)/cytochrome a and the relationship between changes in cellular content of cytochromes and previous observations on respiratory oscillations during the cell cycle are discussed.

Oscillations of enzyme activities during the cell-cycle of a glucose-repressed fission-yeast Schizosaccharomyces pombe 972h-

1. Increased specific activities of cytochrome c oxidase, catalase, succinate dehydrogenase, succinate-cytochrome c oxidoreductase, NADH-cytochrome c oxidoreductase and malate dehydrogenase were observed during glucose de-repression of Schizosaccharomyces pombe. 2. The cell-cycle of this organism was analysed by three different methods: (a) harvesting of cells at intervals from a synchronous culture, (b) separation of cells by rate-zonal centrifugation into different size classes and (c) separation of cells by isopycnic-zonal centrifugation into different density classes. 3. Measurement of enzyme activities during the cell-cycle showed that all the enzymes assayed [cytochrome c oxidase, catalase, acid p-nitrophenylphosphatase, NADH-dehydrogenase, NADH-cytochrome c oxidoreductase, NADPH-cytochrome c oxidoreductase, succinate dehydrogenase, malate dehydrogenase, isocitrate dehydrogenase (NADP) and fumarate hydratase] show periodic expression as ;peaks'. 4. Cytochrome c oxidase shows a single maximum at 0.67 of a cycle, whereas succinate dehydrogenase exhibits two maxima separated by 0.5 of a cell-cycle. 5. All other enzymes assayed showed two distinct maxima per cell-cycle; for catalase, malate dehydrogenase and NADPH-cytochrome c oxidoreductase there is the possibility of multiple fluctuations. 6. The single maximum of cytochrome c oxidase appears at a similar time in the cycle to one maximum of each of the other enzymes studied, except for NADH dehydrogenase. 7. These results are discussed with reference to previous observations on the expression of enzyme activities during the cell-cycle of yeasts.