Augustin Betz

Metabolic control in flow systems

SummaryContinuous infusion of D-glucose, 10-8–10-6 mole/min/g fresh weight, to anaerobic Saccharomyces carlsbergensis cell suspensions induces sustained oscillations of intracellular NADH. Under these conditions the metabolic flux is 100 times less than that after singular addition of an excess of D-glucose. The infused D-glucose is being catabolized except for the periods of rising NADH, where an overshoot in D-glucose concentration occurs shortly before NADH peaks. The oscillatory characteristics under the two conditions are compared.Oscillatory fluctuations in metabolic concentrations are very useful tools in studies on metabolic control in flux systems. But unfortunately rapid damping is observed in yeast suspensions. The infusion technique, as proposed by SelKov (personal communication) was found useful with glycolysing yeast extract (Hess and Boiteux, 1968). Since the cell-free extract of yeast cells varies from day to day with respect to its metabolic and control features, we decided to apply infusion technique to suspension of yeast cells.

Amplitude and period length of yeast NADH oscillations fermenting on different sugars in dependence of growth phase, starvation and hexose concentration

Abstract In yeast cells the dependence of amplitude and period of NADH oscillations on growth phase, starvation time and concentration of hexose fermented (D‐glucose of D‐fructose) has been studied. With both sugars sustained NADH oscillations could be induced during the first logarithmic growth phase only within a small range of starvation time (0.5 to 1.7 h). After transition to diauxic growth on ethanol, oscillations were obtained with D‐glucose from 0.5 to 6 h starvation time, whereas D‐fructose could induce oscillations only after 2 h of starvation. With D‐fructose instead of D‐glucose differences in period lengths of NADH oscillations resulted. These differences after D‐fructose feeding were always consistent and did not depend on the growth phase of the yeast culture. Amplitude and period lengths generally depended on starvation, resulting in stable period lengths after 3 h starvation whereas amplitudes stabilized after 5.3 h. With 0 to 50 mM hexose typical saturation kinetics resulted in amplitude...

Statistical analysis of NADH oscillations in the yeast saccharomyces carlsbergensis fermenting on different sugars

Abstract In order to detect hidden periodicities in glycolytic oscillations and to estimate period lengths the interactive program system TIMESDIA was applied. This program system contains a collection of mathematical procedures apt to the above purpose. The period length of glycolytic oscillations in a suspension of yeast cells depends on the kind of sugar which is fermented by the cells: with each of the four sugars D‐gluctose, D‐fructose, D‐mannose and sucrose different period lengths are obtained. These oscillations are nearly sinusoidal, since in a fourier expansion of the signals the first term exceeds the following ones by at least one order of magnitude. If mixtures of D‐glucose and D‐fructose are added to a cell suspension, the resulting period lengths are between the values which are characteristic for both sugars alone. These oscillations are monotonic too, they are not a superposition of two oscillations different in period length and amplitude, as was shown by the application of our program s...

CONTROL INTERACTIONS AND FLUX RATES IN YEAST GLYCOLYSIS, REVEALED BY METABOLITE OSCILLATIONS

ABSTRACT Transitions from one metabolic state to another (aerobic → anaerobic or starvation → hexose fermentation) are efficient tools for elucidating control sites. In yeast sustained oscillations of metabolite concentrations as a function of endogenous commutations revealed control sites at PFK1), PGK, PK and PDC. In cell free yeast extract fermenting glycogen only ethanol production is constant, whereas the rate of glycogen breakdown is high in the beginning and becomes rather low later on. Metabolite oscillations persist during phases of both high and low influx rates. With trehalose, which yields only 2/3 of the ATP per glucosyl unit compared to glycogen, the flux rate is higher by a factor of 1.5. The flux rates seem to depend on the ATP consumption rate and flux control, localized at PGK, can be distinguished from oscillatory control at PFK. KEYWORDS Glycolysis, glycolytic flux, metabolic control, metabolite oscillations, yeast, yeast glycolysis.

Allosteric activation and competitive inhibition of yeast phosphofructokinase by d-fructose.

Purified phosphofructokinase from bakers yeast is activated by d-fructose in low concentrations (up to 1 mM) and inhibited by high concentrations. The stimulatory effect of d-fructose is similar, but smaller than that of AMP. In the presence of AMP (0.4 mM or higher) d-fructose does no longer stimulate, but its inhibitory effect persists (KI=8 mM). Its dualistic action on phosphofructokinase activity indicates that d-fructose might induce low frequency in glycolytic oscillations by direct interaction with the enzyme.

Peptide des β-Alanins als Ersatz für die freie Aminosäure bei pantothensäurebedürftigen Hefezellen und ihr Verhalten gegenüber dem β-Alanin-Antagonisten Asparagin

ZusammenfassungPantothensäurebedürftige Hefezellen können ihren Bedarf an diesem Vitamin nicht allein aus β-Alanin decken, sondern auch aus Benzoyl-β-Alanin, β-Alanyl-d,l-Norleucin und β-Alanyl-l-Histidin. Der Antagonist Asparagin hemmt die Verwertung dieser Peptide genauso wie diejenige der freien Aminosäure. Durch höhere Konzentrationen an β-Alanin oder β-Alanyl-d,l-Norleucin läßt sich die Hemmwirkung nicht allein kompensieren, es kommt sogar zu einer Förderung des Hefewachstums. Der Antagonist wird dann zum Synergisten.SummaryThe β-alanine containing peptides benzoyl-β-alanine, β-alanyl-d,l-norleucine and β-alanyl-l-histidine can substitute for the amino acid β-alanine in a pantothenic acid requiring yeast. Asparagine, an antagonist of β-alanine, affects these peptides in a similar manner. In combination with an overdose of β-alanine or β-alanyl-d,l-norleucine, asparagine is no longer an antagonist but becomes a synergist.

Peptide des ?-Alanins als Ersatz fr die freie Aminosure bei pantothensurebedrftigen Hefezellen und ihr Verhalten gegenber dem ?-Alanin-Antagonisten Asparagin

Pantothensaurebedurftige Hefezellen konnen ihren Bedarf an diesem Vitamin nicht allein aus β-Alanin decken, sondern auch aus Benzoyl-β-Alanin, β-Alanyl-d,l-Norleucin und β-Alanyl-l-Histidin. Der Antagonist Asparagin hemmt die Verwertung dieser Peptide genauso wie diejenige der freien Aminosaure. Durch hohere Konzentrationen an β-Alanin oder β-Alanyl-d,l-Norleucin last sich die Hemmwirkung nicht allein kompensieren, es kommt sogar zu einer Forderung des Hefewachstums. Der Antagonist wird dann zum Synergisten.