Kinetics of bacteriophage lambda repressor synthesis directed by the PRE promoter: influence of temperature, multiplicity of infection, and mutation of PRM or the cro gene

Summary Expression of the P _RE (establishment) pathway for repressor synthesis is regulated both by phage-specific genetic elements and by physiological conditions. Here we describe the effects of temperature, multiplicity of infection, mutations in the cro gene, and a mutation in P _RM on P _RE-directed repressor synthesis. As Reichardt (1975a) has shown, repressor synthesis begins 5–15 min after infection by wildtype phage, and is shut off at 20–30 min after infection, depending on the temperature. At 43°, synthesis starts sooner, shuts off earlier, and leads to lower repressor levels than are attained at lower temperatures. Experiments with the temperature sensitive mutant crots20 demonstrate that, as had been shown previously in experiments at 30° and 37° C, cro protein is responsible for the shut-off of repressor synthesis at 43°. In addition to the effects of temperature, the kinetics of repressor synthesis are strongly affected by multiplicity of infection (moi). At mois greater than 10, repressor synthesis after infection by wildtype at 30° is dramatically inhibited. Unexpectedly, the P _RM mutation prm116, under certain conditions, can alleviate both cro-mediated shutoff and the inhibition of P _RE-directed repressor synthesis at high moi. These effects of prm116 are observed only at low temperature (30°–32° C) and at mois of about 6–10 or greater; they also appear to be cis-specific. Possible mechanisms for the effects of the prm116 mutation are discussed. Finally, these studies demonstrate that crots20, which was isolated as a temperature-sensitive lethal mutation in the cro gene (Herskowitz, unpublished), is temperature-sensitive with respect to the ability to shutoff P _RE-directed repressor synthesis; however, even at low temperature (30° C), the crots20 gene product is only partially active.     

Repressor synthesis in regulatory mutants of bacteriophage P22

Summary SDS-polyacrylamide gel analysis of P22-infected Salmonella has allowed identification of the c₂ repressor (MW 31,000) and study of repressor synthesis in regulatory mutants of P22. Repressor is synthesized in reduced amounts or is absent in infections with P22, c1#7, P22, c2 am08, P22 c3 am03, and P22 c3 am012, but is synthesized in markedly increased amounts in the virulent mutant, P22 virB3, and its component mutants, vx and k5. Higher levels of repressor are also found in the P22 cly 17 mutant.     

Letter to the Editor: NMR Structure of a Variant 434 Repressor DNA-binding Domain Devoid of Hydroxyl Groups

Abbreviations: 434(1–63) – N-terminal 63-residue DNA-binding domain of the phage 434 repressor; dh434(0–63) – variant 434 repressor DNA-binding domain devoid of hydroxyl groups; P22c2(1–76) – N-terminal 76-residue fragment of the phage P22 c2 repressor; SDS-PAGE – SDS polyacrylamide gel electrophoresis; COSY – correlation spectroscopy; TOCSY – total correlation spectroscopy; NOE – nuclear Overhauser effect; RMSD – root-mean-square deviation.     

Role of energy in oxidative phosphorylation

This article reviews the current status of information regarding the role of energy in the process of oxidative phosphorylation by mitochondria. The available data suggest that in submitochondrial particles (SMP) energy is utilized for the binding of ADP and P_i and for the release of ATP bound at the catalytic sites of F₁-ATPase. The process of ATP synthesis on the surface of F₁ from F₁-bound ADP and P_i appears to be associated with negligible free energy change. The rate of energy production by the respiratory chain modulates the kinetics of ATP synthesis between a lowK _m (for ADP and P_i)-lowV _max mode and a highK _m -highV _max mode. TheK _m extremes for ADP are 2–3 µM and 120–150 µM, andV _max for ATP synthesis at high rates of energy production by bovine-heart SMP is about 440 s^–1 (mole F₁)^–1 at 30°C, which corresponds to 11 µmol ATP (min · mg of protein)^–1. The interaction of dicyclohexylcarbodiimide (DCCD) or oligomycin at the proteolipid (subunitc) of the membrane sector (F₀) of the ATP synthase complex alters the mode of ATP binding at the catalytic sites of F₁, probably to one of lower affinity. It has been suggested that protonic energy might be conveyed to the catalytic sites of F₁ in an analogous manner, i.e., via conformation changes in the ATP synthase complex initiated by proton-induced alterations in the structure of the DCCD-binding proteolipid. Finally, the relationship between the steady-state membrane potential () and the rates of electron transfer and ATP synthesis has been discussed. It has been shown, in agreement with the delocalized chemiosmotic mechanism, that under appropriate conditions is exquisitely sensitive to changes in the rates of energy production and consumption.     

Continuous penicillin G hydrolysis in an electro-membrane reactor with immobilized penicillin G acylase

Penicillin G (2%, w/v in phosphate buffer, pH 8) was hydrolysed in a flow-through, miniature electro-membrane reactor with the penicillin G acylase immobilized in 5% (w/v) polyacrylamide (diam. 10 mm, thickness 2.6 mm, enzyme activity 24 U ml^–1). The conversion of penicillin G increased from 0.15 to almost 0.5 when the electric current applied to the reactor was changed from –600 to +600 A/m² with a substrate residency of 1 h. Symbols and abbreviations c _j ^p & concentration of component j in product stream (M) c _j ^s & concentration of component j in substrate stream (M) c _s ^o & substrate concentration at reactor inlet (M) C _j ^p=c _j ^p/c _S ⁰ & scaled concentration of component j in product stream C _j ^s=c _j ^s/c _S ⁰ & scaled concentration of component j in substrate stream i & electric current density (A/m²) j & reaction component, j P, Q or S P & main reaction product (6-aminopenicillanic acid) PGA & penicillin G acylase Q & side reaction product (phenylacetic acid) S & substrate (penicillin G) Y _s=C _P ^s+C _P ^p & substrate conversion & mean residence time of substrate and product streams in reactor (h) =C _Q ^s+C _Q ^p+C _S ^s+C _S ^s & check-sum of scaled concentrations =C _P ^p/(C _P ^s+C _P ^p) & separation factor of 6-aminopenicillanic acid (0 1)     

Regional variation in canopy transpiration of Central European beech forests

Forest hydrologists have hypothesised that canopy transpiration (E_c) of European temperate forests occurs at rather similar rates in stands with different tree species and hydrologic regimes. We tested this hypothesis by synchronously measuring xylem sap flow in four mature stands of Fagus sylvatica along a precipitation gradient with the aim (1) of exploring the regional variability of annual canopy transpiration (E_c(t)) in this species, and (2) of analysing the relationship between precipitation (P) and E_c(t). E_c(t) rates of 216, 225, 272 and 303 mm year^–1 corresponded to precipitation averages of 520, 710, 801 and 1,040 mm year^–1 in the four stands. We explored the regional variability of E_c(t) in Central European colline to sub-montane beech stands in two meta-analyses based on (1) existing sap flow data on beech (n=5 observations), or (2) all canopy transpiration data on beech obtained by different techniques (sap flow, micrometeorological or soil water budget approaches, n=25). With a coefficient of variation (CV) of 20%, the regional variability of E_c(t) (213–421 mm year^–1) was smaller than the variation in corresponding precipitation (550–1,480 mm year^–1). The mean E_c(t) for beech was 289 (±58) mm year^–1 (n=25). A humped-shaped relationship between E_c(t) and P, with a broad transpiration maximum in the precipitation range from ca. 700 to 1,000 mm year^–1, was found which may indicate soil moisture limitation of transpiration for P –1, and reduced transpiration by increased cloudiness or leaf wetness for P>1,000 mm year^–1. Thus, the precipitation level significantly influences canopy transpiration of humid temperate forests; however, the size of the P influence on E_c(t) and, in part, the direction of its effect differ from forests in semi-arid or arid climates. European beech has the capacity to maintain high E_c rates in both humid and partly dry summer climates (P<550 mm year^–1).     

Regulated expression of plant tRNA genes by the prokaryotic tet and lac repressors

The prokaryotic tet operator (tetO) sequence was inserted at positions upstream and downstream of sequences encoding the Arabidopsis thaliana tRNA _AUC ^Lys or tRNA _AUC ^Trp suppressor tRNAs, and tRNA expression in carrot protoplasts was measured by translational suppression of a nonsense codon in a luciferase reporter gene. Regulation of tRNA expression by the tetracycline repressor (tetR) occurred from genes with the tetO inserted at position –1 (for the tRNA _AUC ^Trp gene), or at positions –2, –6 and –10 (for the tRNA _AUC ^Lys gene), and repression reached 90%. The inducer tetracycline (Tc) restored tRNA expression. Similarly, carrot protoplasts transfected with human tRNA _AUC ^Ser genes containing the lac operator (lacO) in their 5-flanking sequence with or without the lac repressor (lacI) gene, conditionally expressed tRNAs which suppressed the luciferase reporter. Up to 30-fold repression occured by the lactose repressor when lacO was located at position –1 of the tRNA _AUC ^Ser coding sequence. In the presence of the inducer isopropyl--thiogalactoside (IPTG), repression was relieved. These results demonstrate that sequences flanking tRNA genes can strongly influence tRNA expression in plants, and in a conditional fashion when bound by inducible proteins.     

Nitric oxide regulates steroid synthesis by bovine antral granulosa cells in a chemically defined medium

Nitric oxide (NO) in bovine ovary has been characterized as one of the controllers of granulosa cells’ (GC) steroidogenesis and apoptosis. One of the pathways used by NO to have these effects is cGMP. The objectives of the present study were to verify the effect of sodium nitroprusside (SNP), a NO donor, on steroidogenesis, cell viability (mitochondrial activity) and GC cell cycle distribution and if this effect occurs by the NO-cGMP signaling pathway with the addition of SNP with or without 1H-[1,2,3] oxadiaziolo[4,3a]quinoxaline-1-one (ODQ), a selective soluble guanylate cyclase inhibitor. The antral GC from 3 to 5 mm diameter cattle follicles was cultured without treatment (control), with ODQ (10⁻⁴ M) and 10⁻⁵, 10⁻³ and 10⁻¹ M SNP with or without ODQ for 24 h. Nitrate/nitrite (NO₃⁻/N0₂⁻) concentrations were evaluated by Griess method, progesterone (P₄) and 17β-estradiol (E₂) concentrations by chemiluminescence, viability and cell cycle stage by MTT method (3-[4,5-dimethylthiazol-2yl]-2,3 dipheniltetrazolium bromide) and flow cytometry, respectively. Nitrate/nitrite concentration in culture medium increased (P < 0.05) in a dose-dependent manner according to SNP concentration added to the culture medium. The GC cultured without treatment, with ODQ and with 10⁻⁵ M SNP in the presence or absence of ODQ developed into cell aggregates and did not vary in cell viability (P > 0.05), while GC cultured with 10⁻³ and 10⁻¹ M SNP with or without ODQ presented disorganized GC aggregates or did not develop into cell aggregates and also had substantially decreased cell viability (mitochondrial activity inhibition) and steroids synthesis (P < 0.05), and effects were not reversed with us of ODQ. Most GC cultured without treatment (control) or with ODQ, 10⁻⁵ and 10⁻³ M SNP with or without ODQ were in the G0/G1 (80–75%) stage and in a lesser proportion (20–25%) in the S + G2/M stage of the cell cycle, while the 10⁻¹ M SNP treatment resulted in GC in G1 phase arrest. The treatment with 10⁻⁵ M SNP increased (P < 0.05) E₂ synthesis and inhibited (P < 0.05) progesterone synthesis. The addition of ODQ reversed (P < 0.05) the stimulatory effect of 10⁻⁵ M SNP treatment on E₂, but not on P₄ synthesis (P > 0.05). These results demonstrated that E₂ synthesis by antral GC from small follicles is modulated by lesser NO concentrations via the cGMP pathway, but not P₄ while steroids inhibition cGMP pathway independent, mitochondrial damage and the interference on cell cycle progression caused by greater NO concentration can lead to cell death.     

Changes in phosphorus concentrations and pH in the rhizosphere of some agroforestry and crop species

The aim of this work was to assess whether agroforestry species have the ability to acquire P from pools unavailable to maize. Tithonia diversifolia(Hemsley) A. Gray, Tephrosia vogelii Hook f., Zea mays and Lupinus albusL. were grown in rhizopots and pH change and depletion of inorganic and organic P pools measured in the rhizosphere. Plants were harvested at the same growth stage, after 56 days for maize and white lupin and 70 days for tithonia and tephrosia, and the rhizosphere sampled. The rhizosphere was acidified by tithonia (pH change –0.3 units to pH 4.8) and lupins (–0.2 units to 4.9), alkalinised by tephrosia (+0.4 units to pH 5.4), and remained unchanged with maize growth. Concurrent with acidification in the rhizosphere of tithonia there was a decline in resin-P (0.8 g P g^–1). However, there was also a decline in NaOH extractable inorganic P (NaOH-P_i) (5.6 g P g^–1 at the root surface) and organic P pools (NaOH-P_o) (15.4 g P g^–1 at 1.5 mm from the root), which would not be expected without specific P acquisition mechanisms. Alkalinisation of tephrosia rhizosphere was accompanied by changes in all measured pools, although the large depletion of organic P (21.6 g P g^–1 at 5 mm from the root) suggests that mineralisation, as well as desorption of organic P, was stimulated. The size of changes of both pH and P pools varied with distance away from the rhizoplane. Decline of more recalcitrant P pools with the growth of the agroforestry species contrasted with the effect of maize growth, which was negligible on resin-P and NaOH-P_i, but led to an accumulation of P as NaOH-P_o (14.2 g P g^–1 at 5 mm from the root). Overall the depletion of recalcitrant P pools, particularly P_o, suggests that the growth of tithonia and tephrosia enhance desorption and dissolution of P, while also enhancing organic P mineralisation. Both species appear to have potential for agroforestry technologies designed to enhance the availability of P to crops, at least in the short term.     

Thermal inactivation of maltase and its application to temperature-sensitive mutants of yeast

Summary Phage P22 mutationc27 defines a site required for establishment, but not maintenance of repressor synthesis. This study confirms that P22c27 is able to synthesize repressor if active repressor is present. An interaction involving gene products ofc1 andc3 and the sitec27 retards expression of the lytic genes of P22. Mutations in genec1 eliminate the retardation of lytic gene expression, butc27 does not alleviate the retardation. These results are used to construct a model that postulates that binding ofc1 andc3 products to DNA at or nearc27 is sufficient to cause retardation of lytic gene expression. The functioning ofc27 is contrasted to that of the analogouscy mutants of λ. The effect of thec27 mutation upon alleviation of “c1 repression” was studied in a partial revertant ofSalmonella typhimurium Pox-1 in whichc1 repression is exaggerated. The higher frequency of lysogenization seen in the mutant host is related to enhancedc1 repression.     

Cardiac responses to maximal anisotonic isometric contractions during handgrip and leg extension

A group of 14-healthy men performed anisotonic isometric contractions (AIC), for 60 s, at an intensity of 100% maximal voluntary contraction force (MVC) during handgrip (HG) and leg extension (LE). Heart rate (f _c), stroke volume index (SVI) and cardiac output index (Q_cI) were measured during the last 10 s of both AIC by an impedance reography method. Force (F) exerted by the subjects was recorded continuously and reported as a relative force (F _r) (% MVC). The F generated during MVC was greater for LE than for HG (502.I N compared to 374.6 N, P < 0.001). The rate of decrease in F _r was significantly slower for LE than HG for the first 25 s of the exercise (phase 1 of AIC). The F _r developed by the subjects at the end of AIC was 40% MVC for both LE and HG. The increase in f _c was greater for LE (63 beats · min^–1) than for HG (52 beats · min^–1), P < 0.01. The SVI decreased significantly from the resting level by 17.0 ml · m^–2 and by 18.2 ml · m^–2 for LE and HG, respectively. The Q_cI increased insignificantly for HG by 0.091 · min^–1 · m^–2 andsignificantly forLE by 0.561 · min^–1 · m^–2 (P < 0.001). It was concluded that although both AIC caused a significant decrease in SVI, greater increases in f _c and Q_c were observed for LE than for HG. The greater f _c and Q_c reported during LE was probably related to the greater relative force exerted by LE during phase 1 of AIC. It seems, therefore that central command might have dominated for phase 1 of AIC but that the muscle reflex also contributed significantly to the control of the cardiac response to the high intensity AIC.     

Support of1H NMR assignments in proteins by biosynthetically directed fractional13C-labeling

Summary Biosynthetically directed fractional incorporation of¹³C into proteins results in nonrandom¹³C-labeling patterns that can be investigated by analysis of the¹³C–¹³C scalar coupling fine structures in heteronuclear¹³C–¹H or homonuclear¹³C–¹³C correlation experiments. Previously this approach was used for obtaining stereospecific¹H and¹³C assignments of the diastereotopic methyl groups of valine and leucine. In the present paper we investigate to what extent the labeling patterns are characteristic for other individual amino acids or groups of amino acids, and can thus be used to support the¹H spin-system identifications. Studies of the hydrolysates of fractionally¹³C-labeled proteins showed that the 59 aliphatic carbon positions in the 20 proteinogenic amino acids exhibit 16 different types of¹³C–¹³C coupling fine structures. These provide support for the assignment of the resonances of all methyl groups in a protein, which are otherwise often poorly resolved in homonuclear¹H NMR spectra. In particular, besides the individual methyl assignments in Val and Leu, unambiguous distinctions are obtained between the methyl groups of Ala and Thr, and between the - and -methyl groups of Ile. In addition to the methyl resonances, the CH₂ groups of Glu and Gln can be uniquely assigned because of the large coupling constant with the -carbon, and the identification of most of the other spin systems can be supported on the basis of coupling patterns that are common to small groups of amino acid residues.Abbreviations NOE nuclear Overhauser effect - fractional¹³C labeling biosynthetically directed fractional¹³C-labeling - TOCSY total correlation spectroscopy - ROESY rotating frame Overhauser enhancement spectroscopy - [¹³C,¹H]-COSY two-dimensional¹³C–¹H correlation spectroscopy - isotopomer isotope isomer - P22 c2 repressor c2 repressor of the salmonella phage P22 consisting of a polypeptide chain with 216 residues - P22 c2(1-76) N-terminal domain of the P22 c2 repressor with residues 1–76     

Control of lysogenization by phage P22 I. The P22 cro gene

P22 cro^? mutants were isolated as one class of phage P22 mutants (cly mutants) that have a very high frequeney of lysogeny relative to wild-type P22. These mutants: (1) do not form plaques and over-lysogenize relative to wild-type P22 after infection of a wild-type Salmonella host; (2) are defective in anti-immunity; and (3) fail to turn off high-level synthesis of P22 c2-repressor after infection.P22 cro^? mutations are recessive and map between the P22 c2 and c1 genes. P22 cro^? mutations are suppressed by clear-plaque mutations in the c1 gene, one of which is simultaneously cy^?. They are also suppressed, but incompletely, by mutations in the c2 (repressor) gene, especially those that do not completely abolish c2 gene function.Salmonella host mutants have been isolated that are permissive for the lytic growth of the P22 cro^? mutants.     

Modeling of the pyruvate production with<Emphasis Type="Italic"> Escherichia coli</Emphasis> in a fed-batch bioreactor

A family of 10 competing, unstructured models has been developed to model cell growth, substrate consumption, and product formation of the pyruvate producing strain Escherichia coli YYC202 ldhA::Kan strain used in fed-batch processes. The strain is completely blocked in its ability to convert pyruvate into acetyl-CoA or acetate (using glucose as the carbon source) resulting in an acetate auxotrophy during growth in glucose minimal medium. Parameter estimation was carried out using data from fed-batch fermentation performed at constant glucose feed rates of q_VG=10 mL h^–1. Acetate was fed according to the previously developed feeding strategy. While the model identification was realized by least-square fit, the model discrimination was based on the model selection criterion (MSC). The validation of model parameters was performed applying data from two different fed-batch experiments with glucose feed rate q_VG=20 and 30 mL h^–1, respectively. Consequently, the most suitable model was identified that reflected the pyruvate and biomass curves adequately by considering a pyruvate inhibited growth (Jerusalimsky approach) and pyruvate inhibited product formation (described by modified Luedeking–Piret/Levenspiel term).List of symbols c_A acetate concentration (g L^–1) - c_A,0 acetate concentration in the feed (g L^–1) - c_G glucose concentration (g L^–1) - c_G,0 glucose concentration in the feed (g L^–1) - c_P pyruvate concentration (g L^–1) - c_P,max critical pyruvate concentration above which reaction cannot proceed (g L^–1) - c_X biomass concentration (g L^–1) - K_I inhibition constant for pyruvate production (g L^–1) - K_I^A inhibition constant for biomass growth on acetate (g L^–1) - K_P saturation constant for pyruvate production (g L^–1) - K_P inhibition constant of Jerusalimsky (g L^–1) - K_S^A Monod growth constant for acetate (g L^–1) - K_S^G Monod growth constant for glucose (g L^–1) - m_A maintenance coefficient for growth on acetate (g g^–1 h^–1) - m_G maintenance coefficient for growth on glucose (g g^–1 h^–1) - n constant of extended Monod kinetics (Levenspiel) (–) - q_V volumetric flow rate (L h^–1) - q_VA volumetric flow rate of acetate (L h^–1) - q_VG volumetric flow rate of glucose (L h^–1) - r_A specific rate of acetate consumption (g g^–1 h^–1) - r_G specific rate of glucose consumption (g g^–1 h^–1) - r_P specific rate of pyruvate production (g g^–1 h^–1) - r_P,max maximum specific rate of pyruvate production (g g^–1 h^–1) - t time (h) - V reaction (broth) volume (L) - Y_P/G yield coefficient pyruvate from glucose (g g^–1) - Y_X/A yield coefficient biomass from acetate (g g^–1) - Y_X/A,max maximum yield coefficient biomass from acetate (g g^–1) - Y_X/G yield coefficient biomass from glucose (g g^–1) - Y_X/G,max maximum yield coefficient biomass from glucose (g g^–1) - growth associated product formation coefficient (g g^–1) - non-growth associated product formation coefficient (g g^–1 h^–1) - specific growth rate (h^–1) - _max maximum specific growth rate (h^–1)     

Electron transfer in deuterated reaction centers of Rhodobacter sphaeroides at 90 K according to femtosecond spectroscopy data

The primary act of charge separation was studied in P⁺B_A ^– and P⁺H_A ^– states (P, primary electron donor; B_A and H_A, primary and secondary electron acceptor) of native reaction centers (RCs) of Rhodobacter sphaeroides R-26 using femtosecond absorption spectroscopy at low (90 K) and room temperature. Coherent oscillations were studied in the kinetics of the stimulated emission band of P* (935 nm), of absorption band of B_A ^– (1020 nm) and of absorption band of H_A (760 nm). It was found that in native RCs kept in heavy water (D₂O) buffer the isotopic decreasing of basic oscillation frequency 32 cm ^–1 and its overtones takes place by the same factor 1.3 in the 935, 1020, and 760 nm bands in comparison with the samples in ordinary water H₂O. This suggests that the femtosecond oscillations in RC kinetics with 32 cm ^–1 frequency may be caused by rotation of hydrogen-containing groups, in particular the water molecule which may be placed between primary electron donor P_B and primary electron acceptor B_A. This rotation may appear also as high harmonics up to sixth in the stimulated emission of P*. The rotation of the water molecule may modulate electron transfer from P* to B_A. The results allow for tracing of the possible pathway of electron transfer from P* to B_A along a chain consisting of polar atoms according to the Brookhaven Protein Data Bank (1PRC): Mg(P_B)-N-C-N(His M200)-HOH-O = B_A. We assume that the role of 32-cm ^–1 modulation in electron transfer along this chain consists of a fixation of electron density at B_A ^– during a reversible electron transfer, when populations of P* and P⁺B_A ^– states are approximately equal.     

Maximal heart rates and plasma lactate concentrations observed in middle-aged men and women during a maximal cycle ergometer test

The purpose of this study was to investigate criteria for maximal effort in middle-aged men and women undertaking a maximal exercise test until they were exhausted if no measurements of oxygen uptake are made. A large group of 2164 men and 975 women, all active in sports and aged between 40 and 65 years, volunteered for a medical examination including a progressive exercise test to exhaustion on a cycle ergometer. In the 3rd min of recovery a venous blood sample was taken to determine the plasma lactate concentration ([la^–]_{p, 3min}). Lactate concentration and maximal heart rate (f _{c, max}) were lower in the women than in the men (P<0.001). Multiple regression analyses were performed to assess the contribution of sex to [la^–]_{p, 3 min}, independent of age and f _c max, It was found that [la^–]_{p,3 min} was about 2.5 mmol·l^–1 lower in women than in men of the same age and f _{c, max}. In our population 88% of the men and 85% of the women met a combination of the following f _{c, max} and [la^–]_{p, 3min} criteria: f _{c, max} equal to or greater than 220 minus age beats·min^–1 and/or [la^–]_{p, 3min} equal to or greater than 8 mmol·l^–1 in the men and f _{c, max} equal to or greater than 220 minus age beats·min^–1 and/or [la^–]_{p, 3min} equal to or greater than 5.5 mmol·1^–1 in the women.     

Kinetics of reextraction of Penicillin G from the organic phase after reactive extraction

The kinetics of reextraction of penicillin from the LA-2-penicillin complex-n-butylacetate solution by phosphate buffer was investigated experimentally and theoretically. The concentration time functions can be described by a mathematical model in a wide range of pH-values and complex concentrations.List of Symbols a _P [m²/m³] specific interfacial area - c _A , c _Ai [mMol] concentration of amine in the bulk of the organic phase and at the interface - c _AHP , c _AHPi [mMol] concentration of the complex in bulk of the organic phase and at the interface - c _H , c _Hi [mMol] concentration of the proton in the bulk of the aqueous phase and at the interface - c _P , c _Pi [mMol] concentration of the penicillin acid anion in the bulk of the aqueous phase and at the interface - J _A , J _AHP , J _P [mMol · cm · s^–1] fluxes of amine, complex and penicillin acid anion - k _A , k _AHP , k _P [cm · s^–1] mass transfer coefficients of amine, complex and penicillin acid anion - K _G [mMol²] equilibrium constant - t [k] extraction time     

Kinetics of yeast growth and enzyme syntheses in a phosphate-limited continuous culture

Summary The effect of a deficiency of inorganic phosphate on the growth rate and on the invertase and phosphatase activities inSaccharomyces carlsbergensis was studied in a chemostat culture using a synthetic medium in which ethanol was the sole carbon source.The kinetic relationship between the growth rate and both the rates of phosphate uptake and the ethanol consumption agreed well with the threshold model but not the multicative model. The invertase activity of the yeast increased as the dilution rate decreased. As the phosphate concentration in the feed was reduced, the enzyme synthesis increased remarkably. Acid phosphatase activity was repressed completely above a critical molecular ratio, 0.015, of monopotassium phosphate to ethanol in the feed medium. As the phosphate concentration in the feed decreased, the maximum specific enzyme activity increased and the corresponding optimum dilution rate decreased. These experimental changes in enzyme synthesis were expressed mathematically using the modified operon models for enzyme regulation in terms of two fractions of limited inorganic phosphate; one which affects growth and the other which is incorporated in excess by the cells.Nomenclature A ethanol concentration in the culture (mM) - a, b, c, d exponents in the operon model - D dilution rate (h^–1) - E enzyme concentration in the culture (enzyme unit l^–1) - K_a, K_b, K_c, K_d, k equilibrium constants used in the operon model, see Toda (1976b) - o operator gene - P inorganic phosphate concentration in the culture (mM) - Pi limited inorganic phosphate concentration in the cells (mmole inorganic phosphate/g dry weight of cell) - Q specific enzyme activity, no units: (E/X)/(E/X)_max - Q_c, Q_d as defined in Eq. 12 - R repressor - r regulator gene - X cell concentration in the culture (dry cell weight l^–1) Greek Letters molecular ratio of inorganic phosphate to ethanol in the feed medium (mole/mole) - specific growth rate (h^–1) - A specific uptake rate of ethanol (mmole/g cell·h) - P specific uptake rate of inorganic phosphate (mmole/g cell·h) Suffix crit critical value - f feed - max maximum - min minimum - t total - 1, 2 number of species Superfix eff effective for cell growth - exc excess - str structural     

Kinetics of heart rate and catecholamines during exercise in humans The effect of heart denervation

To elucidate the role of factors other than the nervous system in heart rate (f _c) control during exercise, the kinetics off _c and plasma catecholamine concentrations were studied in ten heart transplant recipients during and after 10-min cycle ergometer exercise at 50 W. Thef _c did not increase at the beginning of the exercise for about 60 s. Then in the eight subjects who completed the exercise it increased following an exponential kinetic with a mean time constant of 210 (SEM 22) s. The two other subjects were exhausted after 5 and 8 min of exercise during whichf _c increased linearly. At the cessation of the exercise,f _c remained unchanged for about 50 s and then decreased exponentially with a time constant which was unchanged from that at the beginning of exercise. In the group of eight subjects plasma noradrenaline concentration ([NA]) increased after 30 s to a mean value above resting of 547 (SEM 124) pg · ml^–1, showing a tendency to a plateau, while adrenaline concentration ([A]) did not increase significantly. In the two subjects who became exhausted an almost linear increase in [NA] occurred up to about 1,300 pg · ml^–1 coupled with a significant increase in [A]. During recovery an immediate decrease in [NA] was observed towards resting values. The values of thef _c increase above resting levels determined at the time of blood collection were linearly related with [NA] increments both at the beginning and end of exercise with a similar slope, i.e. about 2.5 beats · min^–1 per 100 pg · ml^–1 of [NA] change. These findings would seem to suggest that in the absence of heart innervation the increase inf _c depends on plasma [NA].     

Kinetics of electron transfer between soluble cytochrome c-554 and purified reaction center complex from the green sulfur bacterium Chlorobium tepidum

Soluble cytochrome c-554 (M _r 10 kDa) is purified from the green sulfur bacterium Chlorobium tepidum. Its midpoint redox potential is determined to be +148 mV from redox titration at pH 7.0. The kinetics of cytochrome c-554 oxidation by a purified reaction center complex from the same organism were studied by flash absorption spectroscopy at room temperature, and the results indicate that the reaction partner of cytochrome c-554 is cytochrome c-551 bound to the reaction center rather than the primary donor P840. The second-order rate constant for the electron donation from cytochrome c-554 to cytochrome c-551 was estimated to be 1.7×10⁷ M^–1 s^–1. The reaction rate was not significantly influenced by the ionic strength of the reaction medium.This revised version was published online in October 2005 with corrections to the Cover Date.