Nejvíce citovaný článek - PubMed ID 2162783
Deuterons cannot replace protons in active transport processes in yeast
The production of organic deuterated compounds in microalgal systems represents a cheaper and more versatile alternative to more complicated chemical synthesis. In the present study, we investigate the autotrophic growth of two microalgae, Chlamydomonas reinhardtii and Desmodesmus quadricauda, in medium containing high doses of deuterated water, D2O. The growth of such cultures was evaluated in the context of the intensity of incident light, since light is a critical factor in the management of autotrophic algal cultures. Deuteration increases the light sensitivity of both model organisms, resulting in increased levels of singlet oxygen and poorer photosynthetic performance. Our results also show a slowdown in growth and cell division processes with increasing D2O concentrations. At the same time, impaired cell division leads to cell enlargement and accumulation of highly deuterated compounds, especially energy-storing molecules. Thus, considering the specifics of highly deuterated cultures and using the growth conditions proposed in this study, it is possible to obtain highly deuterated algal biomass, which could be a valuable source of deuterated organic compounds.
- Klíčová slova
- cell division, deuterated compounds, deuterium, light intensity, microalgae, physical stress,
- Publikační typ
- časopisecké články MeSH
The rare stable isotope of hydrogen, deuterium, has fascinated researchers since its discovery in the 1930s. Subsequent large-scale production of deuterium oxide, commonly known as heavy water, became a starting point for further research. Deuterium exhibits unique physicochemical properties as well as having the strongest kinetic isotope effects among all other elements. Moreover, a broad variety of morphological and physiological changes have been observed in deuterium-treated cells and organisms, including changes in fundamental processes such as cell division or energy metabolism. Even though our understanding of such alterations is still insufficient, it is evident that some of them make growth in a deuterium-enriched environment a challenging task. There seems to be certain species-specific limits to their tolerance to heavy water, where some organisms are unable to grow in heavy water whilst others have no difficulties. Although the effects of deuterium on living organisms are, in general, negative, some of its applications are of great biotechnological potential, as is the case of stable isotope-labelled compounds or deuterated drugs.
Titratable acidity of the extracellular medium was compared with that calculated from pH changes in a suspension of Saccharomyces cerevisiae. After addition of cells to normal water the ratio of titratable acidity to the computed one was about 25, after addition of 50 mmol/L D-glucose it was about 13, after subsequent addition of K+ ions it was only 2. In heavy water the respective values were 30, 9, and 1. Apparently, the principal buffer-generating processes have to do with glucose metabolism but little with the K+/H+ exchange observed after addition of K+. D2O appears to block processes producing the buffering capacity of the medium, among them possibly extrusion of organic acids.
- MeSH
- chlorid draselný farmakologie MeSH
- koncentrace vodíkových iontů MeSH
- kyseliny metabolismus MeSH
- oxid deuteria farmakologie MeSH
- pufry MeSH
- Saccharomyces cerevisiae účinky léků metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- srovnávací studie MeSH
- Názvy látek
- chlorid draselný MeSH
- kyseliny MeSH
- oxid deuteria MeSH
- pufry MeSH
Acidification of the external medium of the yeast Saccharomyces cerevisiae, mainly caused by proton extrusion by plasma membrane H(+)-ATPase, was inhibited to different degrees by D2O, diethylstilbestrol, suloctidil, vanadate, erythrosin B, cupric sulfate and dicyclohexylcarbodiimide. The same pattern of inhibition was found with the uptake of amino acids, adenine, uracil, and phosphate and sulfate anions. An increase of the acidification rate by dioctanoylglycerol also increased the rates of uptake of adenine and of glutamic acid. In contrast, a decrease of the membrane potential at pH 4.5 from a mean of -40 to -20 mV caused by 20 mM KCl had no effect on the transport rates. The ATPase-deficient mutant S. cerevisiae pmal-105 showed a markedly lower uptake of all the above solutes as compared with the wild type, while its membrane potential and delta pH were unchanged. Other types of acidification (spontaneous upon suspension; K+ stimulated) did not affect the secondary uptake systems. A partially competitive inhibition between some individual transport systems was observed, most pronouncedly with adenine as the most avidly transported solute. These observations, together with the earlier results that inhibition of H(+)-ATPase activity affects more the acidic than the basic amino acids and that it is more pronounced at higher pH values and at greater solute concentrations, support the view that it is the protons in or at the membrane, as they are extruded by the ATPase, that govern the rates of uptake by secondary active transport systems in yeast.
- MeSH
- aktivní transport MeSH
- kinetika MeSH
- koncentrace vodíkových iontů MeSH
- membránové potenciály MeSH
- protonové ATPasy antagonisté a inhibitory metabolismus MeSH
- Saccharomyces cerevisiae enzymologie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- protonové ATPasy MeSH
In addition to the general amino acid transport system (GAP) of S. cerevisiae L-tryptophan is transported by another system with approximately 25% capacity of GAP, with a KT of 0.41 +/- 0.08 mmol/L and with a similar specificity as GAP (lower inhibition by Met, Pro, Ser, Thr and 2-aminoisobutyric acid; greater inhibition by Glu and His). The pH optimum of this system is at 5.0-5.5, activation energy above the transition point (20 degrees C) was 20 kJ/mol, below the transition point 55 kJ/mol. The transport by this system was virtually unidirectional, efflux amounting to at most 10% into a tryptophan-free medium. The transport itself was blocked by 2,4-dinitrophenol, antimycin A and uranyl nitrate. The system was synthesized de novo during preincubation with glucose = fructose greater than trehalose greater than ethanol within 30 min, and was degraded with a half-time of 15 min in the absence of further synthesis. The accumulation ratios of L-tryptophan in gap1 mutants were concentration-dependent (200:1 at 1 mumol L-Trp/L, 4:1 at 2.5 mmol L-Trp/L) and decreased with increasing suspension density from 200:1 to 5:1 (for 10 mumol L-Trp/L). The involvement of hydrogen ions in the uptake was clearly demonstrated by the effect of D2O even if it could not be established by either shifts of pHout or membrane depolarization.
- MeSH
- aktivní transport účinky léků MeSH
- anaerobióza MeSH
- citrulin farmakologie MeSH
- koncentrace vodíkových iontů MeSH
- mutace MeSH
- Saccharomyces cerevisiae genetika metabolismus MeSH
- teplota MeSH
- tryptofan metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- citrulin MeSH
- tryptofan MeSH
