Heterozygosity for mutations affecting coat pigmentation in the American mink (<Emphasis Type="Italic">Neovison</Emphasis> vison) enhances structural stability of adrenal cortex under stress conditions

The results of the study of the effects of heterozygosity for mutations affecting coat pigmentation on the response to the environmental stress caused by extreme feeding conditions are provided. The animals with the following genotypes were taken into the study: homozygotes standard (+/+), hedlund white (h/h), and aleutian (a/a) and heterozygotes hedlund white (h/+) and aleutian (a/+). The animals homozygous for the aleutian mutation (a/a) showed a statistically lower growth rate than the animals of other genotypes both in the control and in the experiment (p < 0.05). Under the control conditions, the animals homozygous for both the wild type standard allele (+/+) and the mutant hedlund white (h/h) and aleutian (a/a) alleles showed the evident tendency for the zona fasciculata and zona reticularis of the adrenal cortex broadening compared to the experimental conditions. At the same time, in the animals heterozygous for the hedlund white (h/+) and the aleutian (a/+) mutations, a clear tendency for increasing size of the zona fasciculata and zona reticularis under the experimental conditions was observed. In the heterozygous animals, although we observed single destructive changes in the adrenal cortex under stress conditions, they were much less profound than in the homozygous ones. This may be related to the broader range of morphological adaptation in the heterozygotes, which gives them the possibility of more significant enlargement of the secreting zone to provide for its adequate functioning.     

Effect of four mutations (Cr,S,S(H),h) in genes for mink coat color on brain monoamine oxidase]

Activity of A and B types of monoamine oxidase (MAO) has been investigated in the brain stem and brain hemispheres of mink males of five genotypes for coat-color mutations: standard dark-brown (+/+); heterozygous for the semidominant mutation Black crystal (Cr/+); homozygous for the semidominant mutation Black cross, or "95% White" (S/S); heterozygous for the semidominant mutation Shadow (SH/+); and homozygous for the semirecessive mutation hedlum white (h/h). The main changes in the activity of the A and B MAO types occur in the brain hemispheres. A reduced activity of MAO A has been recorded in the hemispheres of Black crystal minks (Cr/+) and an elevated activity, in the hemispheres of Shadow (SH/+) and 95% White (S/S). The activity of MAO B is reduced in the hemispheres of Black crystal and elevated in the hemispheres of hedlum white (h/h). An increased MAO A activity has also been recorded in the brain stem of Shadow minks (SH/+). It is suggested that genes controlling coat color have a pleiotropic effect on sexual behavior in males and the endocrine function of testicles mediated by a putative change in the metabolism of brain neurotransmitters, substrates of MAOs A and B.     

Karyological study of four Japanese Myotis bats (Chiroptera,Mammalia)

Karyological investigations of four Japanese Myotis species were made based on Gand C-banding pattern analysis. It was revealed that the four species, M. nattereri, M. hosonoi, M. frater kaguyae and M. macrodactylus have all 2n=44 and their karyotypes are, excepting one chromosome pair, identical each other. The only difference in their karyotypes was found on the morphology of the chromosome no. 5. A minute acrocentric (A) was observed in M. nattereri, and a polymorphic (A) and an (M^h) which is a minute metacentric with totally heterochromatic arm was found in M. hosonoi. In M. f. kaguyae, pair no. 5 was a small submetacentric with a totally heterochromatic long arm (SM^h). Polymorphic (SM^h) and (M) which is a small metacentric derived from (SM^h) by a pericentric inversion was seen in M. macrodactylus. Such morphological differentiations of no. 5 were interpreted by assuming an increase of constitutive heterochromatin and also an inversion. The evolutionary pathway in the genus Myotis is assumed to be as follows: (A)(M^h)(SM^h)(M). This assumption was supported by the geographical evidence that the species with the (A) type no. 5 pair is widely distributed in the whole world but the others are restricted to Asia (M^h type) or only to Japan (SM^h and M types).     

Effect of mutations affecting coat color on the blood lymphocyte structure in the american mink (<Emphasis Type="Italic">Mustela vison</Emphasis> Schreber, 1777)

American minks with different genotypes containing the Aleutian coat color allele in the homozygous state, including the single recessive Aleutian (a/a); double recessive sapphire (a/a p/p) and lavender (m/m a/a); triple recessive violet (m/m a/a p/p); and dominant-recessive cross sapphire (S/+ a/a p/p), sapphire leopard (S ^K /+ a/a p/p), and shadow sapphire (S ^H /+ a/a p/p) minks, as well as American minks without the Aleutian allele, including the standard (+/+); single recessive silver-blue (p/p) and hedlund-white (h/h); double recessive pearl (k/k p/p), Finnish topaz (t ^S /t ^S b/b); incompletely dominant royal silver (S ^R /+), standard leopard (S ^K /+), and black crystal (C _R /+); and dominant-recessive snowy topaz (C _R /+ t ^S /t ^S b/b) and Kujtezhyspotted (S ^K /+ b/b) minks have been studied. Homozygosity for the a allele has been found to disturb the subcellular structure of leukocyte, namely the formation of abnormally large granules.     

Brain monoamine oxidase in mink selected for their reaction to man]

Monoamineoxidase activity was studied in minks of three behavioural groups--those bred for absence of aggression towards man, those bred for high aggression to man, and those of non-selected population. Breeding for the absence of aggression was accompanied by a decrease of MAO-B activity with unchanged MAO-A activity. The minks bred for aggressive behaviour towards man, as compared to those bred for the absence of aggression, were characterised by increased MAO-A and MAO-B activities in the brain stem. The effect of emotional stress on MAO-A and MAO-B was similar in aggressive, non-aggressive and unselected minks and was expressed in a decrease of both MAO-A and MAO-B activity. The MAO activity of cerebral hemispheres remained unaffected both by selection for behaviour and by the emotional stress.     

Growth characteristics of a thermotolerant strain of lodderomyces elongisporus grown on sucrose

A thermotolerant yeast species of Lodderomyces elongisporus EH 60 was isolated and physiologically characterized. This yeast possesses a high specific growth rate with μ_max = 0.61 h^?1. The dependence of the specific growth rate and cell yield on temperature, dilution rate, sucrose concentration and pH-value is investigated. Sucrose concentrations greater than 10 g/l inhibit the growth velocity. The specific growth rate μ can be calculated by a simple combination equation in the form: . The total optimum values for a sucrose-based continuous growth process with regard to the optimum cell yeild are: Y_S = 0.50 g DM/g S. T_opt. = 38,6 °C and D_opt. = 0,35 h^?1. The function Y_S = f(D, T) is represented by a total model.     

Modeling 2hJiso(N, N) in nucleic acid base pairs: Ab initio characterization of the 2hJ(N, N) tensor in the methyleneimine dimer as a function of hydrogen bond geometry

The observation of ^2h J _iso(N, N) coupling has prompted considerable interest in this phenomenon from experimentalists and theoreticians due to the potential these couplings hold for the determination of secondary and tertiary structure in biologically important molecules. Here, we present an ab initio (MCSCF) study of the complete ^2h J(N, N) tensor for a model methyleneimine dimer system as a function of (i) the N-N separation, r _NN, and (ii) the hydrogen bond angle, . This simple system models the ^2h J(N, N) tensor of nucleic acid base pairs. Results indicate that although the Fermi-contact mechanism dominates ^2h J _iso(N, N), the coupling tensor is anisotropic due to contributions from the Fermi-contact spin-dipolar cross term. The variation in ^2h J _iso(N, N) as a function of r _NN is fit to an exponential decay. The influence of on the coupling constant is less pronounced but must be considered if experimental coupling constants are to be used for quantitative structure determination. Our results for this simple model system demonstrate that ^2h J _iso(N, N) is a valuable probe of hydrogen bonding in nucleic acid base pairs.     

Effects of growth temperature on maximal specific growth rate,yield, maintenance,and death rate in glucose-limited continuous culture of the thermophilic Bacillus caldotenax

Summary The influence of temperature on the growth of the theromophilic Bacillus caldotenax was investigated using chemostat techniques and a chemically defined minimal medium. All determined growth constants, that is maximal specific growth rate, yield and maintenance, were temperature dependent. It was striking that the very large maintenance requirement was about 10 times higher than for mesophilic cells under equivalent conditions. A death rate, which was very substantial at optimal and supraoptimal growth temperatures, was estimated by comparing the maintenance for substrate and oxygen. There was no indication for a thermoadaptation as postulated by Haberstich and Zuber (1974).Symbols D Dilution rate (h^–1) - D_c=_max Critical dilution rate (h^–1) - E Temperature characteristic (J mol^–1) - k Organism constant - k_d Death rate coefficient (h^–1) - k_m Maintenance substrate coefficient estimated from M_O (h^–1) - M_O Maintenance respiration, mmol O₂ per g dry biomass and h (mmol g^–1h^–1) - M_O Maintenance respiration, taking k_d into account - m_S Maintenance substrate coefficient, g glucose per g dry biomass and h (h^–1) - OD Optical density at 546 nm - QO₂ Specific O₂-uptake rate (mmol g^–1h^–1) - Q _O2 ^V Specific O₂-uptake rate for viable portion of biomass (mmol g^–1 h^–1) - Q_S Specific glucose uptake rate (h^–1) - Q _S ^V Specific glucose uptake rate for viable portion of biomass (h^–1) - R Gas constant 8.28 J mol^–1K^–1 - S Substrate concentration in reactor (g l^–1) - S_O Influent substrate concentration (g l^–1) - T_max Maximal growth temperature (°C) - T_min Minimal growth temperature (°C) - X Dry biomass (g l^–1) - X_tOt=X Dry biomass containing dead and viable cells - X_v Viable portion of biomass - Y _O ^m Potential yield for O₂ corrected for maintenance respiration (g mol^–1) - Y _S ^m Potential yield for substrate corrected for maintenance requirement, g biomass per g glucose (–) - Specific growth rate (h^–1) - _max Maximal specific growth rate (h^–1)     

Growth and respiratory oxidation of reduced sulfur compounds by intact cells ofThiobacillus novellus (type strain) grown on thiosulfate

Thiobacillus novellus (type strain) was grown chemolithoautrophically on thiosulfate in batch cultures under microaerophilic conditions. Under these conditions,T. novellus grew exponentially (=0.05–0.06 h^–1). The respiratory oxidation rates of tetrathionate, thiosulfate, elemental sulfur (S^o), and sulfite were measured respirometrically with an oxygen electrode, with exponentially growing cells. Cells growing on thiosulfate as the unique energy source retain thiosulfate-oxidizing activity, S^o-oxidizing activity (SOA), and very high sulfite-oxidizing activity, but lack respiratory tetrathionate-oxidizing activity. HQNO (50 m), an inhibitor of the quinone-cytochrome b region, strongly inhibited the SOA (70%), moderately the sulfite-oxidizing activity (45%), and poorly the thiosulfate-oxidizing activity (15%), 1mm KCN totally inhibited (>89%) all respiratory activities. This study confirms that inThiobacillus novellus, as well as in otherThiobacilli, SOA is present in cells grown with thiosulfate as sole electron donor. SOA appears not to be an oxygenase; it is linked to the respiratory chain, and the electrons are probably released in the quinone-cytochrome b region.     

On-line parameter and state estimation of continuous cultivation by extended Kalman filter

Summary The on-line estimation of biomass concentration and of three variable parameters of the non-linear model of continuous cultivation by an extended Kalman filter is demonstrated. Yeast growth in aerobic conditions on an ethanol substrate is represented by an unstructured non-linear stochastic t-variant dynamic model. The filter algorithm uses easily accessible data concerning the input substrate concentration, its concentration in the fermentor and dilution rate, and estimates the biomass concentration, maximum specific growth rate, saturation constant and substrate yield coefficient. The microorganismCandida utilis, strain Vratimov, was cultivated on the ethanol substrate. The filter results obtained with the real data from one cultivation experiment are presented. The practical possibility of using this method for on-line estimation of biomass concentration, which is difficult to measure, is discussed.Nomenclature D dilution rate (h^-1) - DO₂ dissolved oxygen concentration (%) - E identity matrix - F Jacobi matrix of the deterministic part of the system equations g - g continuousn-vector non-linear real function - h m-vector non-linear real function - K Kalman filter gain matrix - K _S saturation constant (kgm^-3) - K_S expectation of the saturation constant estimate - M Jacobi matrix of the deterministic part of the measurement equations h - P(t₀) co-variance matrix of the initial values of the state - P(t_k/t_k) c-variance matrix of the error in (t _k|t _k) - P(t_k+1/t_k) co-variance matrix of the error in (t _k+1|t _k - Q co-variance matrix of the state noise - R co-variance matrix of the output noise - S substrate concentration (kgm^-3) - S _i input substrate concentration - t time - t _k discrete time instant with indexk=0, 1, 2,... - u(t) input vector - v(t_k) measurement (output) noise sequence - w(t) n-vector white Gaussian random process - x(t₀) initial state of the system - (t₀) expectation of the initial state values - x(t) n-dimensional state vector - x(t_k) state vector at the time instantt _k - (t_k|t_k) expectation of the state estimate at timet _k when measurements are known to the timet _k - (t_k+1|t_k) expectation of the state prediction - X biomass concentration (kgm^-3) - expectation of the biomass concentration estimate - y(t_k) m-dimensional output vector at the time instantt _k - Y _XIS substrate yield coefficient - _X|S expectation of the substrate yield coefficient estimate - specific growth rate (h^-1) - _M maximum specific growth rate (h^-1) - expectation of the maximum specific growth rate estimate - state transition matrix     

Linkage studies of the h gene with plant weight in flax genotrophs

Summary The association of the H-h (hairy-hairless septa) character with plant weight was studied in the coupling and repulsion phases in F₂ of reciprocal crosses between large (L) and small (S) genotrophs of flax variety Stormont Cirrus. F₂ plants of reciprocal crosses in coupling (L^H x S^h) and in repulsion (L^h x S^H) giving H-h segregations were grown with their parents at two sowing times. Significant positive and negative associations between h and plant weight were obtained. A model is proposed based on the hypothesis that the H phenotype had changed to the h phenotype at the time of induction by a heterochromatic region extending over this locus. In the heterozygote, stable equilibria of the homozygotes are destroyed and transfer of heterochromatin, or number of reiterated sequences, or a decrease in one homologue and an increase in the other, occur in this region between homologous chromosomes. The amount and direction of the association is dependent upon the frequency of transfer: 0% transfer gives complete positive association; 50% transfer, no association; 100% transfer, complete negative association. This mechanism or heterochromatic transfer preserves the Mendelian ratio of 31 of Hh in the F₂. It is also supposed that there must be other controlling elements present as well.     

Phenol degradation by a psychrotrophic strain of Pseudomonas putida

Summary Cell growth and phenol degradation kinetics were studied at 10°C for a psychrotrophic bacterium, Pseudomonas putida Q5. The batch studies were conducted for initial phenol concentrations, S_o, ranging from 14 to 1000 mg/1. The experimental data for 14<=S_o<=200 mg/1 were fitted by non-linear regression to the integrated Haldane substrate inhibition growth rate model. The values of the kinetic parameters were found to be: _m=0.119 h^–1, K _S=5.27 mg/1 and K _I=377 mg/1. The yield factor of dry biomass from substrate consumed was Y=0.55. Compared to mesophilic pseudomonads previously studied, the psychrotrophic strain grows on and degrades phenol at rates that are ca. 65–80% lower. However, use of the psychrotrophic microorganism may still be economically advantageous for waste-water treatment processes installed in cold climatic regions, and in cases where influent waste-water temperatures exhibit seasonal variation in the range 10–30°C.Nomenclature K _S saturation constant (mg/l) - K _I substrate inhibition constant (mg/l) - specific growth rate (h^–1) - _m maximum specific growth rate without substrate inhibition (h^–1) - _max maximum achievable specific growth rate with substrate inhibition (h^–1) - S substrate (phenol) concentration (mg/l) - S_o initial substrate concentration (mg/l) - S_max substrate concentration corresponding to _max (mg/l) - t time (h) - X cell concentration, dry basis (mg DW/l) - X_f final cell concentration, dry basis (mg DW/l) - X_o initial cell concentration, dry basis (mg DW/l) - Y yield factor (mg DW cell produced/mg substrate consumed)     

Uptake and metabolism of GABA in astrocytes cultured from dissociated mouse brain hemispheres

Uptake kinetics and contents of GABA in cultured, normal (i.e. nontransformed) glia cells obtained from the brain hemispheres of newborn mice were measured together with the activity of the GABA transaminase. During three weeks of culturing the activity of the transaminase rose from a low neonatal value toward the level in the adult brain. The uptake kinetics indicated an unsaturable component together with an uptake following Michaelis-Menten kinetics. Both theK _m (40 M) and theV _max (0.350 nmol×min^–1×mg^–1 cell protein) were reasonably comparable to the corresponding values in brain slices, and theV _max was much higher than that reported for other glial preparations. The GABA content was low (<5 nmol/mg cell protein), which is in agreement with the high activity of the GABA transaminase.     

Modulation of inwardly rectifying Na+-K+ channels by serotonin and cyclic nucleotides in salivary gland cells of the leech,Haementeria

Summary The electrically excitable salivary cells of the giant Amazon leech, Haementeria, display a time-dependent inward rectification. Under voltage clamp, hyperpolarizing steps to membrane potentials negative to about –70 mV were associated with the activation of a slow inward current (I _h) which showed no inactivation with time. The time course of activation of I _hwas described by a single-exponential function and was strongly voltage dependent. The activation curve of_hranged from –72 to –118 mV, with half-activation occurring at –100 mV. Ion-substitution experiments indicated that I _his carried by both Na⁺ and K⁺ ions. 5-Hydroxytryptamine (5-HT) increased the amplitude of I _hand its rale of activation. It also produced a positive shift of the activation curve of the conductance underlying I _h G_hwithout altering the slope factor, thus indicating that the voltage dependence of I _hwas modulated by 5-HT. Cs⁺ blocked both I _hand the 5-HT-polentiated current in a voltage-independent manner, whereas Ba²⁺ had little effect. It is concluded that 5-HT increases I _hby modulating the inwardly rectifying Na⁺-K⁺ channels in the salivary cells. The effect of 5-HT may be mediated by an increase in adenylate cyclase activity since I _hwas increased by 8-bromocyclic AMP and by the phosphodiesterase inhibitor, 3-isobutyl-l-methylxanthine. In contrast, I _hwas reduced by 8-bromo-cyclic GMPand by zaprinast (an inhibitor of cyclic GMP-scnsitive phosphodieslerase). Cyclic GMP itself also reduced I _h, and the effect was specific to the 3,5 form; 2,3-cyclic GMP was inactive. The results suggest that the inward-rectifier channel may be modulated in opposite directions by cyclic AMP and cyclic GMPThis work was supported by a grant from the Science and Engineering Research Council (no. GR/F/17087). We are grateful to the SmithKline (1982) Foundation for provision of a pulse generator     

Bestimmung des Heterochromatisierungsstadiums beim white-Positionseffekt mittels r?ntgeninduzierter mitotischer Rekombination in der Augenanlage von Drosophila melanogaster

Summary Position-effect variegation of eye pigmentation in the examined Dp(1;3)N ^264-58 females is due to an insertion of a X-chromosome section including the white-locus into the proximal heterochromatic region of the third chromosome. The light and dark pigmented areas have a cell lineage basis (Fig. 2). Flies bearing the w ⁺-duplication had two X-chromosomes marked with w ^a lz ⁵⁰ e and w ^a rb rux ² respectively (Fig. 3). X-ray induced mitotic recombination in presumptive eye cells of larvae resulted in w ^a lz ^50e /w ^a rb rux ² twin mosaic spots in the adult eyes. After young larvae were treated twin spots appeared, which had one partner light colored and one dark. Such combinations were rarely found after older larvae were treated. Treatment of young larvae in addition produced twin spots with one or both partners variegated (Figs. 5 and 6). Sometime after the stage at which younger larvae were treated and before the stage at which older larvae were treated the translocated w ⁺-gene in each cell was determined for function or no function. As a result the progeny of each of these cells synthesized pigment or not during the pupal stage. At a temperature of 25.5° C the developmental phase during which determination, i.e. heterochromatization of the white gene, takes place, begins not earlier than 39 hours after egg laying and ends about 8 hours later (Fig. 7). In females heterozygous for the short arm of the heterochromatic Y-chromosome linked distally to the X-chromosome (Y ^S X/X) one twin spot partners is homozygous for this arm (Y ^SX/Y^S X), the other lacks it (X/X; Fig.4a). The Y ^SX/Y^S X-partner were more frequently dark pigmented than the X/X-partners (Tables 3 and 4). This shows that heterochromatization of the translocated w ⁺-genes is markedly influenced by the genotype of the single cell. When two genotypes with varied amounts of heterochromatin were compared (Fig. 4) no difference in the phases of heterochromatization could be observed (Table 5). Therefore, when position-effect variegation is modified by varying the amount of heterochromatin in the genome the modification is probably not due to a shift in the phase of heterochromatization.

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Vorgelegt von E. Hadorn     

Performance,kinetics, and substrate utilization in a continuous yeast fermentation with cell recycle by ultrafiltration membranes

Summary A continuous single stage yeast fermentation with cell recycle by ultrafiltration membranes was operated at various recycle ratios. Cell concentration was increased 10.6 times, and ethanol concentration and fermentor productivity both 5.3 times with 97% recycle as compared to no recycle. Both specific growth rate and specific ethanol productivity followed the exponential ethanol inhibition form (specific productivity was constant up to 37.5 g/l of ethanol before decreasing), similar to that obtained without recycle, but with greater inhibition constants most likely due to toxins retained in the system at hight recycle ratios.By analyzing steady state data, the fractions of substrate used for cell growth, ethanol formation, and what which were wasted were accounted for. Yeast metabolism varied from mostly aerobic at low recycle ratios to mostly anaerobic at high recycle ratios at a constant dissolved oxygen concentration of 0.8 mg/kg. By increasing the cell recycle ratio, wasted substrate was reduced. When applied to ethanol fermentation, the familiar terminology of substrate used for Maintenance must be used with caution: it is not the same as the wasted substrate reported here.A general method for determining the best recycle ratio is presented; a balance among fermentor productivity, specific productivity, and wasted substrate needs to be made in recycle systems to approach an optimal design.Nomenclature B Bleed flow rate, l/h - C _T Concentration of toxins, arbitrary units - D Dilution rate, h^-1 - F Filtrate or permeate flow rate, removed from system, l/h - F _o Total feed flow rate to system, l/h - K _s Monod form constant, g/l - P Product (ethanol) concentration, g/l - P _o Ethanol concentration in feed, g/l - PP} Adjusted product concentration, g/l - PD Fermentor productivity, g/l-h - R Recycle ratio, F/F _o - S Substrate concentration in fermentor, g/l - S _o Substrate concentration in feed, g/l - V Working volume of fermentor, l - V _MB Viability based on methylene blue test - X Cell concentration, g dry cell/l - X _o Cell concentration in feed, g/l - Y _ATP Cellular yield from ATP, g cells/mol ATP - Y _ATPS Yield of ATP from substrate, mole ATP/mole glucose - Y _G True growth yield or maximum yield of cells from substrate, g cell/g glucose - Y _P Maximum theoretical yield of ethanol from glucose, 0.511 g ethanol/g glucose - Y _P/S Experimental yield of product from substrate, g ethanol/g glucose - Y _x/s Experimental yield of cells from substrate, g cell/g glucose - S _NP/X Non-product associated substrate utilization, g glucose/g cell - k ₁, k₂, k₃, k₄ Constants - k ₁ ^APP , k ₂ ^APP Apparent k ₁, k₃ - k ₁ ^TRUE True k ₁ - m Maintenance coefficient, g glucose/g cell-h - m ^* Coefficient of substrate not used for growth nor for ethanol formation, g glucose/g cell-h - Specific growth rate, g cells/g cells-h, reported as h^-1 - _m Maximum specific growth rate, h^-1 - v Specific productivity, g ethanol/g cell-h, reported as h^-1 - v _m Maximum specific productivity, h^-1     

Phosphate-limited growth of Chromatium vinosum in continuous culture

Chromatium vinosum DSM 185 was grown in continuous culture at a constant dilution rate of 0.071 h^-1 with sulfide as the only electron donor. The organism was subjected to conditions ranging from phosphate limitation (S _R-phosphate=2.7 M and S _R-sulfide=1.8 mM) to sulfide limitation (S _R-phosphate=86 M and S _R-sulfide=1.8 mM). At values of S _R-phosphate below 7.5 M the culture was washed out, whereas S _R-phosphate above this value resulted in steady states. The saturation constant (K ) for growth on phosphate was estimated to be between 2.6 and 4.1 M. The specific phosphorus content of the cells increased from 0.30 to 0.85 mol P mg^-1 protein with increasing S _R-phosphate. The specific rate of phosphate uptake increased with increasing S _R-phosphate, and displayed a non-hyperbolic saturation relationship with respect to the concentration of phosphate in the inflowing medium. Approximation of a hyperbolic saturation function yielded a maximum uptake rate (V _max) of 85 nmol P mg^-1 protein h^-1, and a saturation constant for uptake (K _t) of 0.7 M. When phosphate was supplied in excess 8.5% of the phosphate taken up by the cells was excreted as organic phosphorus at a specific rate of 8 nmol P mg^-1 protein h^-1.Non-standard abbreviations BChla bacteriochlorophyll a - D dilution rate; _max, maximum specific growth rate - maximum specific growth rate if the substrate were not inhibitory - K saturation constant for growth on phosphate - V _max maximum rate of phosphate uptake - K _i saturation constant for phosphate uptake - K _i inhibition constant for growth in the presence of sulfide - S _R concentration of substrate in the inflowing medium     

Biochemical and genetic factors in the heat inactivation of murine β-glucuronidase

The enzymes coded for by two alleles at the glucuronidase structural locus (Gus) were compared in their response to pH, buffering anion, buffer molarity, ionic strength, and temperature. The heat-labile Gus^h gene product responded in a qualitatively similar but quantitatively reduced manner compared to the relatively heat-stable Gus ^b gene product. In all buffers tested, the enzyme was most heat stable at pH 5.0. Ranking of the various buffer anions tested, according to increasing heat stabilization, was water acetate phosphate < citrate. Varying the molarity of the buffers from 0.01 to 0.6 m at pH 5.0 revealed further differences among the buffers. Increasing ionic strength exerted a destabilizing force on the protein. The half-life of the enzyme decreased by as much as a hundredfold between 71 and 75 C. The Gus^h/Gus^h genotype also results in decreased activity levels in all tissues, reportedly because of decreased synthesis. The heat inactivation curves of Gus^b/Gus^h heterozygotes were incompatible with any theoretical curve based on the assumption that the Gus^b and Gus^h chromosomes in the heterozygote behave in a manner similar to that seen in the homozygotes.This research was supported by a Basil O'Connor Starter Research Grant from the National Foundation—March of Dimes (R. J. M.) and by a grant from The Jane Coffin Childs Memorial Fund for Medical Research (K. H.).Fellow of The Jane Coffin Childs Memorial Fund for Medical Research.     

Influence of pH,lactose and lactic acid on the growth of Streptococcus cremoris: a kinetic study

Summary The effect of various culture conditions on growth kinetics of an homofermentative strain of the lactic acid bacterium Streptococcus cremoris were investigated in batch cultures, in order to facilitate the production of this organism as a starter culture for the dairy industry. An optimal pH range of 6.3–6.9 was found and a lactose concentration of 37 g·l^-1 was shown to be sufficient to cover the energetic demand for biomass formation, using the recommended medium. The study of the effect of lactic acid concentration on growth kinetics revealed that the end-product was not the sole factor affecting growth. The strain was characterized for its tolerance towards lactic acid and a critical concentration of 70 g·l^-1 demonstrated. With the product yield of 0.9 g·g^-1 at non-lactose limiting conditions the lactic acid concentration of 33 g·l^-1 could not explain the low growth rates obtained, implicating a nutritional limitation.Symbols t _f fermentation duration (h) - X Biomass concentration (g·l^-1) - X _m maximum biomass concentration (g·l^-1) - S lactose concentration (g·l^-1) - S _r residual lactose concentration (g·l^-1) - P produced lactic acid concentration (g·l^-1) - P _a added lactic acid concentration (g·l^-1) - P _c critical lactic acid concentration (g·l^-1) - specific growth rate (h^-1) - _max maximum specific growth rate (h^-1) - R _x/S biomass yield (g·g^-1) calculated when =0 - R _P/S product yield (g·g^-1)