Electrophoretic pseudopolymorphism: the role of modifications illustrated by proteolysis

The term "pseudopolymorphism" refers to a situation, where there is no simple correspondence between genotype and phenotype: a single genotype may be moulded into several phenotypes. It is known that broad substrate specificity of enzymes may be one of the causes for pseudopolymorphism. This article deals with the other cause for this phenomenon--a consequence of post-translation modifications, such as limited proteolysis. Variability of some enzymes of grass carp Ctenopharyngodon idella Val. (Pisces, Cyprinidae) was studied by gel electrophoresis. It was found that variability of isozyme patterns of lactate dehydrogenase (LDH), glucose-6-phosphate dehydrogenase (G-6-PDH), malic enzyme (ME) and esterase (EST) is connected with the differences in protease activity of grass carp liver homogenates. The fish isozyme patterns of high (and, partially, intermediate) proteinase activity had some anomalies: displacement of fractions, one or several additional fractions, decreased activity of single fractions or the whole spectrum. In some cases, this variability looked like a classical polymorphic system specified by two alleles of one locus. The effect of enzymes' and proteins' modifications on electrophoretical pseudopolymorphism is discussed.     

Kinetics of ligand binding to a cluster of membrane-associated receptors

The process of ligand binding to a cluster of membrane-associated receptors is examined theoretically. The theoretical model proposed involves the diffusion of ligands from the solution to the disc-like cluster of receptors on the surface of the spherical cell. When the ligand hits the internal part of the disc-like cluster, it begins to move laterally until it leaves the disc through its outer surface or is bound by one of the receptors inside the disc. If the ligand leaves the cluster, it returns to the solution and hits the disc again after a certain period, etc. According to our model the transition from a diffusion-limited to a reaction-limited process of binding is determined by the dimensionless parameter Dt _c/a ², where D is the lateral diffusion coefficient,t _c is the characteristic time of reaction, anda is the radius of the disc-like cluster. The forward rate constantk _f turns out to be a function of . Comparing the results of our calculations ofk _f with some experimental data we found that agreement is achieved at high , i.e. the process of ligand binding by clustered receptors is predominantly reaction-limited.     

Hofmeister effect in ion transport: reversible binding of halide anions to the roflamycoin channel.

We have studied the anion-dependent gating of roflamycoin ion channels using spectral analysis of noise in currents through multichannel planar lipid bilayers. We have found that in addition to low frequency current fluctuations that may be attributed to channel switching between open and closed conformations, roflamycoin channels exhibit a pronounced higher frequency noise indicating that the open channel conductance has substates with short lifetimes. This noise is well described by a Lorentzian spectrum component with a characteristic cutoff frequency that depends on the type of halide anions according to their position in the Hofmeister series. It is suggested that transitions between the substates correspond to a reversible ionization of the channel by a penetrating anion that binds to the channel structure, more chaotropic anions being bound for longer times. Within a framework of a two-substate model, the duration of the substate with reduced electrostatic barrier for cation current varies exponentially with anion electron polarizability. This explains two features of the roflamycoin channel reported earlier: the increase in apparent single-channel conductance along the series F- < Cl- < Br- < I- and the reverse of channel selectivity from anionic for KF to cationic for KI.     

Asymmetry of syringomycin E channel studied by polymer partitioning

To probe the size of the ion channel formed by Pseudomonas syringae lipodepsipeptide syringomycin E, we use the partial blockage of ion current by penetrating poly(ethylene glycol)s. Earlier experiments with symmetric application of these polymers yielded a radius estimate of approximately 1 nm. Now, motivated by the asymmetric non-ohmic current-voltage curves reported for this channel, we explore its structural asymmetry. We gauge this asymmetry by studying the channel conductance after one-sided addition of differently sized poly(ethylene glycol)s. We find that small polymers added to the cis-side of the membrane (the side of lipodepsipeptide addition) reduce channel conductance much less than do the same polymers added to the trans-side. We interpret our results to suggest that the water-filled pore of the channel is conical with cis- and trans-radii differing by a factor of 2-3 and that the smaller cis-radius is in the 0.25-0.35 nm range. In symmetric, two-sided addition, polymers entering the pore from the larger opening dominate blockage.     

The coupled variability of quantitative and qualitative traits: a single-locus 3-allele model

Statistics for estimation of additive and non-additive effects of marker gene on quantitative trait are developed from the mad-model of a quantitative trait for three-allelic codominant marker locus. All they may be obtained directly from population data, without any hybridological experiments.     

Comparative evaluation of diagnostic preparations

The diagnostic value of preparations is commonly characterized by sensitivity and specificity. But not all these characteristics make it possible to decide unequivocally which of the preparations to be compared is superior to the other one with respect to its diagnostic value. It is proposed that in the choice of a diagnostic preparation its capacity to provide data for exact diagnosis should be considered, i.e. the additional characteristic indicating the spread of the disease under study. As an example, the comparison of the diagnostic value of conventional methods and the polymerase chain reaction in the diagnostics of helicobacteriosis is presented. The described method for the evaluation of the diagnostic value of the preparation is well-grounded, simple and obvious.