Ribosomes in growing and non-growing bacterial cells

1. 1.
   It was found that growing cells always contained more different groups of ribosomes and their total amount was greater than in non-growing cells or spores, in which only two ribosome groups with different sedimentation constants, according to the species of microorganism, were consistently found.     
   
   

Transport protein synthesis in non-growing yeast cells

Addition of a metabolizable substrate (glucose, ethanol and, to a degree, trehalose) to non-growing baker's yeast cells causes a boost of protein synthesis, reaching maximum rate 20 min after addition of glucose and 40–50 min after ethanol or trehalose addition. The synthesis involves that of transport proteins for various solutes which appear in the following sequence: H⁺, l-proline, sulfate, l-leucine, phosphate, α-methyl-d-glucoside, 2-aminoisobutyrate. With the exception of the phosphate transport system, the K_t of the synthesized systems is the same as before stimulation. Glucose is usually the best stimulant, but ethanol matches it in the case of sulfate and exceeds it in the case of proline. This may be connected with ethanol's stimulating the synthesis of transport proteins both in mitochondria and in the cytosol while glucose acts on cytosolic synthesis alone. The stimulation is often repressed by ammonium ions (leucine, proline, sulfate, H⁺), by antimycin (proline, trehalose, sulfate, H⁺), by iodoacetamide (all systems tested), and by anaerobic preincubation (leucine, proline, trehalose, sulfate). It is practically absent in a respiration-deficient petite mutant, only little depressed in the op₁ mutant lacking ADP/ATP exchange in mitochondria, but totally suppressed (with the exception of transport of phosphate) in a low-phosphorus strain. The addition of glucose causes a drop in intracellular inorganic monophosphate by 30%, diphosphate by 45%, ATP by 70%, in total amino acids by nearly 50%, in transmembrane potential (absolute value) by about 50%, an increase of high-molecular-weight polyphosphate by 65%, of total cAMP by more than 100%, in the endogenous respiration rate by more than 100%, and a change of intracellular pH from 6.80 to 7.05. Ethanol caused practically no change in ATP, total amino acids, endogenous respiration, intracellular pH or transmembrane potential; a slight decrease in inorganic monophosphate and diphosphate and a sizeable increase in high-molecular-weight polyphosphate. The synthesis of the various transport proteins thus appears to draw its energy from different sources and with different susceptibility to inhibitors. It is much more stimulated in facultatively aerobic species (Saccharomyces cerevisiae, Endomyces magnusii) than in strictly aerobic ones (Rhodotorula glutinis, Candida parapsilosis) where an inhibition of transport activity is often observed after preincubation with metabolizable substrates.     

Glucose turnover in adult non-growing tumour-bearing mice

[6-3H]glucose was used for measurements of plasma glucose turnover in adult non-growing mice with sarcoma-induced malnutrition. Plasma glucose turnover was increased in freely-fed tumour-bearing mice but not in starved tumour-bearing mice. Elevated glucose turnover in freely-eating sarcoma-bearing mice was associated with an increased glucose pool, the latter not only being due to an expanded distribution volume of glucose. Plasma lactate was elevated in sarcoma-bearing mice independently of their food intake. The results show that elevated plasma glucose turnover in an anorectic tumour-bearing host is not due to insufficient adaptation to food depression. Increased glucose turnover in tumour-bearing mice was associated with an altered intermediary whole body metabolism of glucose which is not entirely accounted for by the state of malnutrition of the host.     

Intracellular protein breakdown in non-growing cells of Escherichia coli

1. When Escherichia coli leu(-) was incubated at 35 degrees in a medium based on minimal medium, but with the omission of phosphate ions, or glucose, or NH(4) (+) ions and leucine, intracellular protein was degraded at a rate of about 5%/hr. in each case. If Mg(2+) ions were omitted, however, the rate of degradation was 2.9%/hr. 2. Under certain conditions of incubation, protein degradation was inhibited. The inhibitor was neither NH(4) (+) ions nor amino acids, and its properties were not those of a protein, but it might be an unstable species of RNA. 3. Although a large part of the cell protein was degraded at about 5%/hr. during starvation of NH(4) (+) ions and leucine, some proteins were lost at more rapid rates, whereas others were lost at lower rates or not at all. 4. In particular, beta-galactosidase activity was lost at about 8%/hr. during starvation of NH(4) (+) ions and leucine, whereas d-serine-deaminase and alkaline-phosphatase activities were stable. During starvation of Mg(2+) ions, all three enzyme activities were stable.     

RNA turnover and protein synthesis in fish cells

Protein synthesis in fish has been previously correlated with RNA content. The present study investigates whether protein and RNA synthesis rates are similarly related. Protein and RNA synthesis rates were determined from ³H-phenylalanine and ³H-uridine incorporation, respectively, and expressed as % · day⁻¹ and half-lives, respectively. Three fibroblast cell lines were used: BF-2, RTP, CHSE 214, which are derived from the bluegill, rainbow trout and Chinook salmon, respectively. These cells contained similar RNA concentrations (∼175 μg RNA · mg⁻¹ cell protein). Therefore differences in protein synthesis rates, BF-2 (31.3 ± 1.8)>RTP (25.1 ± 1.7)>CHSE 214 (17.6 ± 1.1), were attributable to RNA translational efficiency. The most translationally efficient RNA (BF-2 cells), 1.8 mg protein synthesised · μg⁻¹ RNA · day⁻¹, corresponded to the lowest RNA half-life, 75.4 ± 6.4 h. Translationally efficient RNA was also energetically efficient with BF-2 cells exploiting the least costly route of nucleotide supply (i.e. exogenous salvage) 3.5–6.0 times more than the least translationally efficient RNA (CHSE 214 cells). These data suggest that differential nucleotide supply, between intracellular synthesis and exogenous salvage, constitutes the area of pre-translational flexibility exploited to maintain RNA synthesis as a fixed energetic cost component of protein synthesis. Accepted: 12 November 1999     

Hydantoinase activity of immobilized non-growing Pseudomonas putida cells

Summary Hydantoinase (dihydropyrimidinase E.C. 3.5.2.2) activity of Pseudomonas putida DSM 84 was evaluated using cells immobilized in alginate beads and in a microporous hollow fibre bioreactor. Conversion of dihydrouracil into N-carbamyl--alanine was most efficient with alginate-immobilized cells. A 40 to 45% conversion was obtained in shake flasks and in continuous mode with packed bed columns. The highest volumetric productivity was obtained with a packed bed column operated at a dilution rate of 0.5 h^-1 (99 g of product. 100 l^-1 per hour). After 96 h the alginate beads began to swell and break apart; no free cells were detected however. Despite some initial loss of cells from the microporous hollow fibre bioreactor, a steady state was later established and maintained for 400 h at dilution rates of 0.1 and 0.25 h^-1.     

Degradation and replenishment of the labile protein fraction in non-growing cells of the asporogenic mutant ofBacillus megaterium

Kinetics of degradation of labelled proteins was followed in two asporogenic mutants ofBacillus megaterium during incubation in a sporulation medium. Both the mutant producing exocellular protease (KM 1prn ⁺) and the mutant not producing the enzyme (KM 12prn) were found to contain a labile protein fraction, whose proportion decreases with prolonged time of labelling and whose half-life is about 1 h. Most proteins were relatively stable and were degraded at a rate of 1 %/h and 2 %/h in strains KM 1 and KM 12, respectively (half life 70–80 h and 35–40 h in strains KM 1 and KM 12, respectively). The intracellular proteolytic activity of the KM 12 mutant remains practically the same during incubation in the sporulation medium or slowly increases. The labile protein fraction practically disappears from the cells after a 3.5-h incubation. When such a culture is then subjected to a shift-up and transferred again to the sporulation medium, the rate of protein turnover temporarily increases. The temporary increase of the turnover rate is caused by a partial replenishment of the labile protein fraction rather than by an accelerated degradation of the relatively stable fraction. The intracellular proteolytic activity does not increase under these conditions. The wild sporogenic strain ofB. megaterium also contains the labile protein fraction. Its half protein life is 1 h or less. However, the second protein fraction is degraded much more rapidly than in the asporogenic mutants and its half life is 6–7 h.     

Ferritin iron kinetics and protein turnover in K562 cells

The binding, incorporation, and release of iron by ferritin were investigated in K562 cells using both pulse-chase and long term decay studies with 59Fe-transferrin as the labeled iron source. After a 20-min pulse of labeled transferrin, 60% of the 59Fe was bound by ferritin with the proportion increasing to 70% by 4 h. This initial binding was reduced to 35% when the cells were exposed to the chelator desferrioxamine (5 mM) for an additional 30 min. By 4 h the association of 59Fe with ferritin was unaffected by the presence of the chelator, and levels of 59Fe-ferritin were identical to those in control cells (70%). Between 4-10h there was a parallel decline in 59Fe-ferritin in both control and desferrioxamine-treated cells. When incoming iron was bound by ferritin it was, therefore, initially chelatable but with time progressed to a further, nonchelatable compartment. In turnover studies where ferritin was preloaded with 59Fe by overnight incubation, 50% of the label was released from the protein by 18 h, contrasting with a t 1/2 for cellular iron release of approximately 70 h. The half-time of 59Fe release from ferritin was accelerated to 11 h by the presence of desferrioxamine. The half-time for ferritin protein turnover determined by [35S]methionine labeling was approximately 12 h in the presence or absence of the chelator. Thus, when the reassociation of iron with ferritin was prevented by the exogenous chelator there was a concordant decay of both protein and iron moieties. The direct involvement of lysosomes in this turnover was demonstrated by the use of the inhibitors leupeptin and methylamine which stabilized both 59Fe (t 1/2 = 24 h) and 35S (t 1/2 = 25.6 h) labels. We conclude that in this cell type the predominant mechanism by which iron is released from ferritin is through the constitutive degradation of the protein by lysosomes.     

A proteolytic system in growing and non-growing cells ofEscherichia coli

1. (1)
   Escherichia титр клетки содер жат протеазы Система разделения собственных белков в качестве равно как казеин с символикой (вс131) Я на несколько ще лочного рН. Темпы про теолиза не заметно влияют ethylenediaminotetraacetic кислоту или iodoacetic кисло та, п-chlormercuribenzoate снижает темп ы гидролиза (su131) Я казеи н, но ее эффект не може т быть отменено цист еина.     
   
   

Control of respiration rate in non-growing cells of Paracoccus denitrificans.

By means of fluorimetric measurement and by direct determination of intracellular NAD+ and NADH contents, it was proved that the respiration rate of Paracoccus denitrificans cells utilizing glucose is limited by processes preceding NADH oxidation in the respiratory chain, so that the membrane NADH dehydrogenase is not saturated by its substrate. In the separated membrane fraction on saturation with exogenous NADH the main limiting factor is represented by NADH: ubiquinone oxidoreductase.     

Regulation of protein turnover by L-glutamine in porcine intestinal epithelial cells

L-Glutamine (Gln) plays an important role in sustaining the intestinal mucosal mass of humans and animals. However, the underlying mechanisms are largely unknown. This study tested the hypothesis that Gln regulates protein turnover in intestinal epithelial cells. Intestinal porcine epithelial cells (IPEC-1) were cultured for 3 h (short-term study) or 96 h (long-term study) in Gln-free Dulbecco's modified Eagle-F12 Ham medium containing 0, 0.5 or 2.0 mM Gln. To determine effects of ammonia (a metabolite of Gln, i.e., 0.18 mM ammonia produced from 2 mM Gln in 3 h) on protein turnover, additional experiments were conducted in which medium contained 0.5 mM Gln and 0, 0.2, 0.5 or 2.0 mM NH(4)Cl. Variables of analysis included cell growth, protein synthesis, proteolysis and mammalian target of rapamycin (mTOR) signaling. IPEC-1 cell growth increased with extracellular Gln concentrations. Compared with 0 mM Gln, the addition of 0.5 and 2 mM Gln to medium stimulated protein synthesis and inhibited protein degradation in those cells in both the short- and long-term studies. Ammonia (0.05 to 2.0 mM) did not affect protein synthesis, although higher levels of ammonia (0.5 and 2.0 mM) reduced protein degradation in IPEC-1 cells. Consistent with the data on protein turnover, 0.5 and 2 mM Gln increased abundance of phosphorylated eIF4E-binding protein-1 and phosphorylated S6 kinase-1 proteins. Collectively, these results demonstrate that physiological levels of Gln regulate protein turnover independent of ammonia production in intestinal cells through the mTOR signaling pathway.     

Proteasome-dependent turnover of protein disulfide isomerase in oxidatively stressed cells.

Generalized increases in protein oxidation and protein degradation in response to mild oxidative stress have been widely reported, but only a few individual proteins have actually been shown to undergo selective, oxidation-induced proteolysis. Our goal was to find such proteins in Clone 9 liver cells exposed to hydrogen peroxide. Using metabolic radiolabeling of intracellular proteins with [35S]cysteine/methionine, and analysis by two-dimensional polyacrylamide gel electrophoresis (2-D PAGE), we found at least three labeled proteins ("A," "B," and "C") whose levels were decreased significantly more than the generalized protein loss after mild oxidative stress. "Protein C" was excised from 2-D PAGE and subjected to N-terminal amino acid microsequencing. "Protein C" was identified as Protein Disulfide Isomerase or PDI (E.C. 5.3.4.1), and this identity was reconfirmed by Western blotting with a C-terminal anti-PDI monoclonal antibody. A combination of quantitative radiometry and Western blotting in 2-D PAGE revealed that PDI was selectively degraded and then new PDI was synthesized, following H2O2 exposure. PDI degradation was blocked by inhibitors of the proteasome, and by cell treatment with proteasome C2 subunit antisense oligonucleotides, indicating that the proteasome was largely responsible for oxidation-induced PDI degradation.