Respiratory oscillations and heat evolution in synchronous cultures of Candida utilis

Synchronous cultures of the budding yeast Candida utilis prepared by continuous-flow size selection showed respiratory oscillations when the energy source was either glucose, acetate or glycerol. The period of the oscillations was about one-third of the cell cycle time (i.e. about 0.5 h). No fluctuations in heat evolution could be detected. In organisms growing with acetate or glycerol, the effects of cyanide, N,N'-dicyclohexylcarbodi-imide and carbonyl cyanide m-chlorophenylhydrazone (maximum inhibition of respiration at respiratory maxima, maximum uncoupling of energy conservation at respiratory minima) suggest that the control mechanism responsible for the oscillations is mitochondrial respiratory control in vivo. The effects of cyanide and N,N'-dicyclohexylcarbodi-imide on the respiration of cultures growing synchronously with glucose were different from those for cultures growing with the non-fermentable substrates; this suggests that the mitochondrial respiratory system interacts with the early reactions of glucose utilization.     

Kinetics of recA function in conjugational recombinant formation.

Summary Genetic recombination was studied in F^- strains of E. coli carrying a mutation (recA200) that confers a thermosensitive Rec^- phenotype. Recombination during Hfr matings at 35C was monitored by raising the temperature of incubation to 42C at various intervals so that only merozygotes that had completed those functions dependent on the activity of the recA gene product could form recombinant progeny. The results indicated that no more than 1–2% of the merozygotes present while mating was in progress were able to form recombinant colonies at 42C. Separation of mating pairs reduced the yield of recombinants obtained at 35C by 50 to 200-fold if plating on agar medium was delayed for 15–30min by continuing incubation in broth medium. recA200 merozygotes that were also recB21 sbcB15 proved relatively stable when plating was delayed in this manner, which suggested that Hfr DNA is prone to exonuclease inactivation in recA200 merozygotes after mating pairs have separated. Post-mating incubation in high salt medium or on agar plates promoted the recovery of recombinants at 35C. However, the majority of recA200 merozygotes did not acquire the ability to form recombinant colonies at 42C under these more stable conditions until mating pairs had been separated and incubation continued at 35C for 40–60 min. It was concluded that recA200 strains are partially defective for recombination even at low temperature but that terminating mating promotes the recovery of recombinants. A mechanism involving the stimulation of RecA activity by mating pair separation is postulated to account for the efficient recovery of recombinants from HfrxF^- recA200 crosses at 35C.     

Enzyme induction in rat liver: The effects of Be2+ in vivo

Rats given an LD₅₀ dose of Be²⁺ showed reduced activities of ornithine decarboxytase and tyrosine aminotransferase in liver in response to dexamethasone induction. Control fed animals showed superinduction. Be²⁺ also inhibited the uptake of [³H]orotic acid into rapidly labelled RNA of ribonucleoprotein particles extracted from liver nuclei in isomolar solutions at pH 8.0. Consistent with inhibition of cytoplasmic protein kinase reported previously (Kaseret at., 1980), the uptake of [³²P]P_i into proteins in the ribonucleoprotein particles was also diminished.     

Rapid isolation of plasma membranes in high yield from cultured fibroblasts.

1. A method was developed which allows the rapid preparation of pure plasma membranes in high yield from cultured fibroblasts. 2. Cells are lysed in hypo-osmotic borate/EDTA and, after differential centrifugation, the membranes collected by centrifugation on a sucrose barrier. 3. Electron microscopy of the isolated material shows large membrane vesicles essentially free from contaminating organelles. 4. There is no detectable activity of the endoplasmic-reticulum enzyme marker, NADH2--lipoamide oxidoreductase (EC 1.6.4.3), and that of succinate dehydrogenase (EC 1.3.99.1), a marker for mitochondria, is substantially decreased. Chemical compositions are in good agreement with previous observations. 5. This study confirms the usefulness of applied isotopic markers for isolating plasma membranes.     

The cytochromes of Acanthamoeba castellanii.

1. Low-temperature difference spectra of gradient-purified mitochondria of Acanthamoeba castellanii reveal the presence of cytochromes b-555, b-562 and c-549, with a-type cytochromes having a broad asymmetrical maximum at 602 nm; these components were also observed in specta of whole cells. 2. The a-type cytochromes are unusual in that they have split Soret absorption maxima (at 442 and 449 nm) and an uncharacteristic CO difference spectrum. 3. CO difference spectra of whole cells and 'microsomal' membranes show large amounts of cytochrome P-420 compared with cytochrome P-450. 4. Difference spectra in the presence of cyanide indicate the presence of an a-type cytochrome and two cyanide-reacting components, one of which may be cytochrome a3. 5. Whole-cell respiration in a N2/O2 (19:1) atmosphere was decreased by 50%, suggesting the presence of a low-affinity oxidase. This lowered respiration is inhibited by 50% by CO, and the inhibition is partially light-reversible; photochemical action spectra suggest that cytochrome a3 contributes to this release of inhibition. Other CO-reacting oxidases are also present. 6. The results are discussed with the view that cytochrome a3 is present in A. castellanii, but its identification in CO difference spectra is obscured by other component(s).     

The influence of snow conditions on the date of breeding of wading birds in north-east Greenland

The young of wading birds that breed in some parts of the arctic hatch when their insect food supply is most abundant. This appears to be the ultimate factor determining the date of egg-laying. In various other arctic birds the date of breeding may be influenced, directly or indirectly, by the time at which snow or ice melts. The Joint Biological Expedition to N.E. Greenland 1974 studied Ringed plovers Charadrius hiaticula , Dunlins Calidris aplina , Sanderlings Calidris alba , Knots Calidris canutus , and Turnstones Arenaria interpres breeding in various areas within 80 km of each other.
In 1974 the thaw was two or three weeks later than normal in the region. The time at which snow cleared and the dates of breeding of the waders differed considerably between valleys: breeding was delayed in valleys that cleared late. In all areas egg-laying ceased early in July, probably because chicks hatching from eggs laid later would not be ready to migrate by the end of the summer. Hence the mean date and length of the egg-laying period were determined by the date of snow clearance from the breeding areas.
Studies of the potential food resources indicate that the waders in N.E. Greenland do not appear to time their breeding so that the young hatch at some peak of food abundance. Sufficient food resources are probably available over a long period of time.