THE SORPTION OF BACTERIOPHAGE BY LIVING AND DEAD SUSCEPTIBLE BACTERIA : I. EQUILIBRIUM CONDITIONS

The above data relating to the antistaphylococcus phage and single strain of S. aureus with which previous papers have been concerned (9, 10, 11, 12), bring out the following points. (a) For live, resting, susceptible B suspended in broth as well as for B in a P-B mixture during the logarithmic phases of B growth and P formation, P is distributed in a manner typical of numerous materials soluble in both phases of a two phase system, i.e., distribution proceeds in accordance with the equation C_b/C_a = K where C_b = extracellular P/ml. of broth and C_a = intracellular P/ml. of B. The combination is quantitatively reversible. (b) With heat-killed, susceptible B, P distribution is of the adsorptive type, expressible in the form of the adsorption isotherm equation a = kC ^1/n. The average value of 1/n is 0.80 in agreement with the results of von Angerer (2). Under ordinary conditions dead B take up much more P than do live B, the reaction proceeding to > 99 per cent completion. The combination of P with dead B is not demonstrably reversible and with high initial P/B ratios saturation of B with P is effected. Bacteria killed at 65°C., 80°C. and 100°C. show no differences in adsorptive ability. (c) The rates at which live, resting, susceptible B and heat-killed, susceptible B remove P from solution do not differ significantly. Velocity constants of the process calculated from See PDF for Equation agree satisfactorily. It is shown that the time interval consumed is concerned with an actual reaction between P and B and not with diffusion of P through the broth to B. (d) P determinations have been found to serve as satisfactory indicators for B growth in P-B mixtures where [B] is to be maintained at a constant level. Very small increments in [B] give rise to measurable increases in P by virtue of the fact that dP/dt is proportional to a power of the rate dB/dt (9). (e) Similarly [P] estimations will detect death of B cells in P-live B suspensions. Dead B take up large amounts of P irreversibly; such P cannot function in the titration and the result is a sharp drop in [P] of controls.     

Probabilistic Model of Microbial Cell Growth,Division, and Mortality

After a short time interval of length δt during microbial growth, an individual cell can be found to be divided with probability P_d(t)δt, dead with probability P_m(t)δt, or alive but undivided with the probability 1 − [P_d(t) + P_m(t)]δt, where t is time, P_d(t) expresses the probability of division for an individual cell per unit of time, and P_m(t) expresses the probability of mortality per unit of time. These probabilities may change with the state of the population and the habitat''s properties and are therefore functions of time. This scenario translates into a model that is presented in stochastic and deterministic versions. The first, a stochastic process model, monitors the fates of individual cells and determines cell numbers. It is particularly suitable for small populations such as those that may exist in the case of casual contamination of a food by a pathogen. The second, which can be regarded as a large-population limit of the stochastic model, is a continuous mathematical expression that describes the population''s size as a function of time. It is suitable for large microbial populations such as those present in unprocessed foods. Exponential or logistic growth with or without lag, inactivation with or without a “shoulder,” and transitions between growth and inactivation are all manifestations of the underlying probability structure of the model. With temperature-dependent parameters, the model can be used to simulate nonisothermal growth and inactivation patterns. The same concept applies to other factors that promote or inhibit microorganisms, such as pH and the presence of antimicrobials, etc. With P_d(t) and P_m(t) in the form of logistic functions, the model can simulate all commonly observed growth/mortality patterns. Estimates of the changing probability parameters can be obtained with both the stochastic and deterministic versions of the model, as demonstrated with simulated data.     

THEORY AND MEASUREMENT OF VISUAL MECHANISMS : X. MODIFICATIONS OF THE FLICKER RESPONSE CONTOUR,AND THE SIGNIFICANCE OF THE AVIAN PECTEN

1. When there is projected on the retina (man, monocularly) the shadow of a grid which forms a visual field in several distinct pieces (not including the fovea in the present tests), the ordinary properties of the flicker recognition contour (F vs. log I) as a function of the light-time cycle fraction (t_L) can be markedly disturbed. In the present experiments flicker was produced by the rotation of a cylinder with opaque vertical stripes. In the absence of such a grid shadow the "cone" segments of the contours form a set in which F_max. and the abscissa of inflection are opposite but rectilinear functions of t_L, while the third parameter of the probability integral (σ''_{log I}) remains constant. This is the case also with diverse other animals tested. In the data with the grid, however, analysis shows that even for low values of t_L (up to 0.50) there occurs an enhancement of the production of elements of neural effect, so that F_max. rises rather than falls as ordinarily with increase of t_L, although σ''_{log I} stays constant and hence the total number of acting units is presumed not to change. This constitutes valid evidence for neural integration of effects due to the illumination of separated retinal patches. Beginning at t_L = 0.75, and at 0.90, the slope of the "cone" curve is sharply increased, and the maximum F is far above its position in the absence of the grid. The decrease of σ''_{log I} (the slope constant) signifies, in terms of other information, an increase in the number of acting cone units. The abscissa of inflection is also much lowered, relatively, whereas without the grid it increases as t_L is made larger. These effects correspond subjectively to the fact that at the end-point flicker is most pronounced, on the "cone" curve, along the edges of the grid shadow where contrast is particularly evident with the longer light-times. The "rod" portion of the F - log I contour is not specifically affected by the presence of the grid shadow. Its form is obtainable at t_L = 0.90 free from the influence of summating "cone" contributions, because then almost no overlapping occurs. Analysis shows that when overlapping does occur a certain number of rod units are inhibited by concurrent cone excitation, and that the mean contribution of elements of neural action from each of the non-inhibited units is also reduced to an extent depending on the degree of overlap. The isolated "rod" curve at t_L = 0.90 is quite accurately in the form of a probability integral. The data thus give a new experimental proof of the occurrence of two distinct but interlocking populations of visual effects, and experimentally justify the analytical procedures which have been used to separate them. 2. The changing form of the F - log I contour as a function of t_L, produced in man when the illuminated field is divided into parts by a shadow pattern, is normally found with the bird Taeniopygia castenotis (Gould), the zebra finch. The retina has elements of one general structural type (cones), and the F - log I contour is a simplex symmetrical probability integral. The eye of this bird has a large, complex, and darkly pigmented pecten, which casts a foliated shadow on the retina. The change in form of the F - log I curve occurs with t_L above 0,50, and at t_L = 0.90 is quite extreme. It is more pronounced than the one that is secured in the human data with the particular grid we have used, but there is no doubt that it could be mimicked completely by the use of other grids. The increase of flicker acuity due to the pecten shadow is considerable, when the dark spaces are brief relative to the light. The evidence thus confirms the suggestion (Menner) drawn from comparative natural history that the visual significance of the avian pecten might be to increase the sensory effect of small moving images. It is theoretically important that (as in the human experiment) this may be brought about by an actual decrease of effective retinal area illuminated. It is also significant theoretically that despite the presence of shadows of pecten or of grid, and of the sensory influences thus introduced, the probability integral formulation remains effective.     

Steroidumwandelnde enzyme aus mikro-organismen—VIII. Einfluβ organischer lösungsmittel unterschiedlicher hydrophobizität auf die bindung an der affinitätsmatrix-affinitätschromatographie einer 4-en-3-oxo-steroid: (akzeptor)-1-en-oxidoreduktase aus Nocardia opaca

In the presence of organic solvents the biospecific adsorption of a 4-en-3-oxosteroid: (acceptor)-l-enoxidoreductase (EC 1.3.99.4.) from Nocardia opaca on an immobilized testosterone ligand was investigated. Between hydrophobicity of the solvent and the matrix-binding of enzyme a quantitative relation was found. Thus a linear correlation was obtained of the logarithmic relation of matrix bound and free enzyme activity (log B) with the logarithms of the distribution coeffizient in the system octanol/ water (log P) of the organic solvents: log B = 0.002 (±0.067) + 0.300 (±0.051) log P. Thus a further quantitative relation was obtained for affinity chromatography and for investigation of the nature of biospecific interaction between steroid ligand and protein.     

Penicillium oxalicum S-adenosylmethionine synthetase is essential for the viability of fungal cells and the expression of genes encoding cellulolytic enzymes

As the universal methyl donor for methylation reactions, S-adenosylmethionine (AdoMet) plays an indispensable role in most cellular metabolic processes. AdoMet is synthesized by AdoMet synthetase. We identified the only one AdoMet synthetase (PoSasA) in filamentous fungus Penicillium oxalicum. PoSasA was widely distributed in mycelium at different growth stages. The absence of PoSasA was lethal for P. oxalicum. The misregulation of the PoSasA encoding gene affected the synthesis of extracellular cellulolytic enzymes. The expression levels of cellobiohydrolase encoding gene cbh1/cel7A, β-1-4 endoglucanase eg1/cel7B, and xylanase encoding gene xyn10A were remarkably downregulated as a result of decreased PosasA gene expression. The production of extracellular cellulases and hemicellulases was also reduced. By contrast, the overexpression of PosasA improved the production of extracellular cellulases and hemicellulases. A total of 133 putative interacting proteins with PoSasA were identified using tandem affinity purification and mass spectrometry. The results of functional enrichment on these proteins showed that they were mainly related to ATP binding, magnesium ion binding, and ATP synthetase activity. Several methyltransferases were also observed among these proteins. These results were consistent with the intrinsic feature of AdoMet synthetase. This work reveals the indispensable role of PoSasA in various biological processes.     

Photoreactions of bacteriopheophytins and bacteriochlorophylls in reaction centers of Rhodopseudomonas sphaeroides and Chloroflexus aurantiacus

A comparison of spectral properties of reaction centers from Chloroflexus aurantiacus and Rhodopseudomonas sphaeroides (R-26) is reported. Treatment of reaction centers from Rps. sphaeroides with NaBH₄ leads to a decrease of the dipole strength of the 800-nm band by factor of approx. 1.75-1.95 and to the formation of new bacteriopheophytin, BPh-715, which is almost completely removed during the purification of reaction centers. The modification of the reaction centers does not change the quantum yield of P photooxidation and the spectrum of BPh-545 (H₁) photoreduction which includes the changing of the 800-nm band. This implies the preservation of the photoactive chain P-B₁-H₁-Q_A (where B₁ is the bacteriochlorophyll (BChl)-800 molecule situated between P and H₁) and the modification of the second BChl-800 (B₂). The preparation of modified reaction centers is a mixture of at least three types of reaction centers with different contents of B₂ and of the second BPh (H₂). Some of the reaction centers (5-25%) contain the original B₂ and H₂ molecules (type I). In the CD spectrum of modified reaction centers a decrease of the 800-nm band and the appearance of a positive band at 765 nm is observed. This spectrum is similar to the CD spectrum of Chloroflexus reaction centers containing 3 BPh's and 3 BChl's. This implies that in some (approx. 40%) of the modified Rps. sphaeroides reaction centers (type II) B₂ has been replaced by BPh a which interacts with H₂. Probably some of the modified reaction centers (approx. 40%) have lost both B₂ and H₂ (type III). The modification of reaction centers leads to a considerable decrease of the CD bands at 800 (+) nm and 810 (−) nm and to a decrease of the absorbance changes near 800 nm in the difference absorption spectrum of the oxidation of P. The data are interpreted in terms of the interaction between P and B₁ molecules which gives two transitions at 790-800 and 810 nm with different orientations in modified Rps. sphaeroides as well as in Chloroflexus reaction centers. Similar transitions are observed for the interaction between P and B₂. The spectral analysis shows the existence of two chains P-B₁-H₁, and P-B₂-H₂ in which the distances between the centers of molecules are 1.3 nm or less.     

Improvement of trans-sialylation versus hydrolysis activity of an engineered sialidase from Trypanosoma rangeli by use of co-solvents

Biocatalytic trans-sialylation is relevant for the design of biomimetic oligosaccharides such as human milk oligosaccharides. t-Butanol and ionic liquids, EAN (ethylammonium nitrate), [MMIm][MeSO₄] (1,3-dimethylimidazolium methyl sulfate), and [C₂OHMIm][PF₆] (1-(2-hydroxyethyl)-3-methylimidazolium hexafluorophosphate), were examined as co-solvents for the improvement of the synthesis versus hydrolysis ratio in the trans-sialylation of lactose, catalysed by an engineered sialidase from Trypanosoma rangeli. The use of 25 % (v/v) t-butanol as co-solvent significantly increased 3′-sialyllactose production by 40 % from 1.04 ± 0.09 to 1.47 ± 0.01 mM. The synthesis versus hydrolysis ratio increased correspondingly by 1.2-times. 1–2.5 % (v/v) EAN or [C₂OHMIm][PF₆] improved the synthesis versus hydrolysis ratio up to 2.5-times but simultaneously decreased the 3′-sialyllactose yield, probably due to enzyme inactivation caused by the ionic liquid. [MMIm][MeSO₄] had a detrimental effect on the trans-sialylation yield and on the ratio between synthesis and hydrolysis.     

Qualitative aspects of thyroglobulin antibodies in Hashimoto's thyroiditis and Graves' disease

We have tried to characterize the thyroglobulin antibodies (TgAb) involved in Hashimoto''s thyroiditis and Graves'' disease by studying their affinity constants and binding capacities. Two populations of antibodies were found in half of the patients with either disease, TgAb₁ with a high affinity (K₁) but a low binding capacity (B₁) and TgAb₂ with a lower affinity (K₂) but a much higher binding capacity (B₂). The mean affinity constants and binding capacities were similar in the two diseases. In the other half of the patients only one population of antibody was present, with a low affinity constant (K_t) and a very high binding capacity (B_t), thus comparable to TgAb₂. The mean K_t and B_t were similar in the two diseases. From these results it would appear that circulating thyroglobulin antibodies in Hashimoto''s thyroiditis and Graves'' disease are similar in their affinity constants and binding capacities, so that these characteristics do not reflect the different pathogenesis of each condition.     

Axial ligation constants of [5,10,15,20-tetraphenylporphyrinato(2-)] cobalt

Axial ligation constants (log K^B) of bases for [5, 10,15,20-tetraphenylporphyrinato(2-)]cobalt ([Co^II (tpp)]) are reported. The log K^B values of pyridine derivatives except for 4-cyanopyridine show a good linear relationship in a plot of log K^B vs. pK_a of the axial ligand. 4-Cyanopyridine gives a larger log K^B than expected. The log K^B value of 1-methylimidazole for [Co^II(tpp)] is almost the same as that for tetrakis(p-methoxyphenyl)porphyrinatocobalt(II) ([Co((p-CH₃O)tpp)]), althoug the other log K^B values for [Co^II(tpp)] are always slightly larger than those for [Co((p-CH₃O)tpp)]. These results are discussed on the basis of the σ- and π-bonding abilities of the bases, and the solvent effects on the log K^B values. The lower base affinities of cobalt(II) capped porphyrins are also discussed.     

Growth and reproduction of eyestalk ablated penaeus canaliculatus (Olivier, 1811) (crustacea:Penaeidae)

The effects of single (unilateral) eyestalk ablation on the growth and reproduction of male and female Penaeus canaliculatus (Olivier) were compared with those of unablated (control) individuals. Prawns ≤ 10 mm in carapace length ablated in the premoult stage suffered high mortality. Prawns recognized as immature when ablated always moulted irrespective of their moulting stage; ovaries in females did not become vitellogenic nor did spermatogenesis occur in males. Mature females ablated in the premoult stage underwent moulting while those in the postmoult stage developed mature ovaries. Mature males in the postmoult or intermoult stages took longer to moult than those that were in the premoult stage when ablated. The Von Bertalannfy equations describing growth in P. canaliculatus were as follows: L_t = 25.6 [1−e^{−0.0756(t−t_o)}]for ablated males; L_t = 25.3 [1−e^{−0.059(t−t_o)}] for unablated males; L_t= 37.2 [1−e^{−0.048(t−t_o)}] forablated females; L_t = 33.4 [1−e^{−0.044(t−t_o)]} for unablated females. Differences in the growth rates were a result of both the moulting frequency and the increment in size at moult. However, the relative contribution of these two factors to growth varied with sex as well as with size. In both sexes, ablated individuals became sexually mature earlier; females spawned earlier. Although moulting frequency and the total number of spawns were greater for ablated females, the mean number of eggs produced (per spawn as well as total) by unablated females was higher and the mean hatching success was better.     

Intrinsic viscosities of polyelectrolytes in the absence and in the presence of extra salt: Consequences of the stepwise conversion of dextran into a polycation

Viscosities of dilute polymer solutions were measured in capillary viscometers for samples varying in their fraction f of charged units from 0.00 to 0.90. The dependence of the logarithm of the relative viscosity on polymer concentration c is in all cases reproduced quantitatively by three characteristic parameters: [η], the intrinsic viscosity; B, a viscometric interaction parameter (related to the Huggins constant); [η], a parameter required only for polyelectrolytes at low concentrations of extra salt. In pure water [η] increases more than 80 times as the fraction f rises from zero to 0.90 and [η] starts from zero and goes up to ≈71 mL/g. Upon the addition of NaCl [η] decreases by at least one order of magnitude (depending on the value of f). The observed dependences of log [η] on log c_salt can be modeled quantitatively by Boltzmann sigmoids.     

Equilibrium and structural studies of silicon(IV) and aluminium(III) in aqueous solution. 12. A potentiometric and 29Si-NMR study of silicon tropolonates

Complexation in the H⁺-Si(OH)₄-tropolone (HL) system was studied in 0.6 M (Na)Cl medium at 25° C. Speciation and formation constants were determined from potentiometric (glass electrode) and ²⁹Si-NMR data. Experimental data cover the ranges 1.5 ? - log[H⁺] ? 8.4, 0.002 ? B ? 0.012 M, and 0 ? C ? 0.060 M (B and C stand for the total concentration of Si and tropolone, respectively). In acid solutions (-log[H⁺] ? 3) a hexacoordinated cationic complex, SiL₃⁺, is formed with log K(Si(OH)₄ + 3HL + H⁺ XXX SiL₃⁺ + 4H₂O) = 7.08 ± 0.03. Furthermore, the formation of a disilicic acid was established from ²⁹Si-NMR data. The dimerization constant of Si(OH)₄ was found to be 10 exp (1.2 ± 0.1). In model calculations the solubility of quartz and amorphous SiO₂ in the presence of tropolone is demonstrated. Data were analyzed using the least-squares computer program LETAGROPVRID.     

THE INACTIVATION OF BACTERIOPHAGE BY MERCURY BICHLORIDE; THE REACTIVATION OF BICHLORIDE-INACTIVATED PHAGE

1. The inactivation of antistaphylococcus bacteriophage suspended in infusion broth at pH 7.6 and 22°C. by HgCl₂ proceeds according to the equation dP/dt = k [HgCl₂] [P_o – P_i] over the range studied. 2. This inactivation can be reversed by precipitation of Hg⁺⁺ with H₂S. In the present experiments the inactivation was carried out until only some 5 per cent of the initial phage remained active. After reactivation the [P] had increased to 100 per cent of the initial [P].     

A method to calculate binding equilibrium concentrations in the allosteric ternary complex model that supports ligand depletion

The allosteric ternary complex model is frequently used in pharmacology to represent the interaction of a receptor R with two ligands A and B. Certain well-known formulas are routinely used to calculate the fractions of the receptor bound at equilibrium with A only, B only, and both A and B. However, it is often omitted that these classical formulas presume that there is no ligand depletion, i.e. that the equilibrium concentrations [A] and [B] of the ligands are well approximated by their total concentrations [A]_T and [B]_T. We present a calculation method which is applicable without this or any restrictions. The equilibrium concentration [R] of the receptor is implicitly characterized by an equation which is solved with a very simple convergent numerical algorithm. The concentrations [A] and [B] are given by explicit formulas in terms of [R]. The required parameters are the equilibrium dissociation constants K_A and K_B, the cooperativity factor α, and the total concentrations [R]_T, [A]_T and [B]_T.     

CRITICAL ILLUMINATION AND FLICKER FREQUENCY,AS A FUNCTION OF FLASH DURATION: FOR THE SUNFISH

From the relations between critical illumination in a flash (I_m) and the flash frequency (F) for response of the sunfish to visual flicker when the proportion of light time to dark time (t_L/t_D) in a flicker cycle is varied at one temperature (21.5°) the following results are obtained: At values of t_L/t_D between 1/9 and 9/1 the F - log I_m curves are progressively shifted toward higher intensities and lower F_max.. F_max. is a declining rectilinear function of the percentage of the flash cycle time occupied by light. The rod and the cone portions of the flicker curve are not shifted to the same extent. The cone portion and the rod region of the curve are each well described by a probability integral. In terms of F as 100 F/F_max. the standard deviation of the underlying frequency distribution of elemental contributions, summed to produce the effect proportional to F, is independent of t_L/t_D. The magnitude of log I_m at the inflection point (r''), however, increases rectilinearly with the percentage light time in the cycle. The proportionality between I_m and σ_II1 is independent of t_L/t_D. These effects are interpreted as consequences of the fact that the number of elements of excitation available for discrimination of flicker is increased by increasing the dark interval in a flash cycle. Decreasing the dark interval has therefore the same kind of effect as reducing the visual area, and not that produced by decreasing the temperature.     

Halplotypes of the ovine ADRB3 gene (ADRB3) and their association with post-weaning growth in New Zealand Suffolk sheep

The β₃-adrenergic receptor (ADRB3) regulates thermogenesis and lipolysis in brown and white adipose tissue. Previously, sixteen ovine ADRB3 haplotypes have been defined. In this study, the relationship between these ADRB3 haplotypes and variation in post-weaning growth was investigated in 797 New Zealand Suffolk lambs from 38 sire lines and eight studs, using PCR-SSCP and General Linear Mixed-effects Models. Seven haplotypes were found in these sheep and they comprised five previously reported intron sequences and four previously reported 3′UT sequences. The frequencies of the various diplotypes ranged from 0.1 to 17.6 % and individual haplotypes from 0.8 to 32.5 %. The presence of haplotype A-b was associated with a decreased weaning-weight (P = 0.001). Sheep with the B-c/F-e diplotype had a higher mean weaning-weight than those with A-b/B-c or A-b/E-e (P < 0.05). The presence of C-a was found to be associated with increased post-weaning growth (P = 0.008), while the presence of B-c was associated with decreased post-weaning growth (P = 0.005). Sheep with A-b/C-a had higher mean post-weaning growth than those with A-b/A-b, A-b/B-c, B-c/B-c, B-c/E-e or B-c/F-e (P < 0.05). Sheep with B-c/B-c had lower mean post-weaning growth than those with A-b/C-a or B-c/C-a (P < 0.05). Additive effects for the different forms of the B-c haplotypes on post-weaning growth were identified. The effects of the ovine ADRB3 haplotypes on weaning-weight and post-weaning growth confirm that they could be used as a candidate gene-marker for improving sheep growth.     

THE FLICKER RESPONSE CONTOURS FOR GENETICALLY RELATED FISHES. II

The flicker response contour has been determined for several species and types of the teleosts Xiphophorus (X.) and Platypoecilius (P.) under the same conditions. The curve (F vs. log I_m) is the same for representatives of each generic type, but is different for the two genera. Its duplex nature is analyzable in each instance by application of the probability integral equation to the rod and cone constituent parts. The parameters of this function provide rational measures of invariant properties of the curves, which have specific values according to the genetic constitution of the animal. The F ₁ hybrids (H'''') of X. montezuma x P. variatus show dominance of the X. properties with respect to cone F_max. and σ'' _{log I}, but an intermediate value of the abscissa of inflection (τ''). The rod segment shows dominance of σ'' _{log I} from P., but an intermediate value of F_max. and of τ''. The composite flicker curve involves the operation of two distinct assemblages of excitable elements, differing quantitatively but not qualitatively in physicochemical organization, probably only secondarily related to the histological differentiation of rods and cones because almost certainly of central nervous locus, but following different rules in hereditary determination, and therefore necessarily different in physical organization. The interpretation of the diverse behavior of the three parameters of the probability summation is discussed, particularly in relation to the physical significance of these parameters as revealed by their quantitative relations to temperature, retinal area, and light time fraction in the flash cycle, and to their interrelations in producing the decline of rod effects at higher intensities. It is stressed that in general the properties of the parameters of a chosen interpretive analytical function must be shown experimentally to possess the physical properties implied by the equation selected before the equation can be regarded as describing those invariant properties of the organic system concerned upon which alone can deduction of the nature of the system proceed. The importance of genetic procedures in furthering demonstration that the biological performance considered in any particular case exhibits constitutionally invariant features provides a potentially powerful instrument in such rational analysis.     

Quantitative description of morphological changes during growth of a pleomorphic budding bacterium

Temporal variations in the different morphological forms observed during growth of the pleomorphicHyphomicrobium T37 have been quantified by the use of a “Population Index” (P _i). This index relates the “Cell Number” (CN) in each “Colony-Forming Unit” (CFU) to the total number of CFU's at any particular time. Such measurements have proved of value in explaining the nature of an observed pseudo-log phase in swarmer-inoculated cultures and of a discontinuity in the log phase of growth.     

Decreased binding capacity (B max) of muscarinic acetylcholine receptors in fibroblasts from boys with attention-deficit/hyperactivity disorder (ADHD)

Monoaminergic dysregulation is implicated in attention-deficit/hyperactivity disorder (ADHD), and methylphenidate and amphetamines are the most frequently prescribed pharmacological agents for treating ADHD. However, it has recently been proposed that the core symptoms of the disorder might be due to an imbalance between monoaminergic and cholinergic systems. In this study, we used fibroblast cell homogenates from boys with and without ADHD as an extraneural cell model to examine the cholinergic receptor density, that is, muscarinic acetylcholine receptors (mAChRs). We found that the binding capacity (B _max) of [³H] Quinuclidinyl benzilate (³H-QNB) to mAChRs was decreased by almost 50 % in the children with ADHD (mean = 30.6 fmol/mg protein, SD = 25.6) in comparison with controls [mean = 63.1 fmol/mg protein, SD = 20.5, p ≤ 0.01 (Student’s unpaired t test)]. The decreased B _max indicates a reduced cholinergic receptor density, which might constitute a biomarker for ADHD. However, these preliminary findings need to be replicated in larger ADHD and comparison cohorts.