Factors determining the reconstructive denaturation of proteins in sodium dodecyl sulfate solutions. Further circular dichroism studies on structural reorganization of seven proteins

The factors determining the onset and extent of reconstructive denaturation of proteins were considered by comparing circular dichroism (CD) data of seven proteins and previously published findings. The effects of sodium dodecyl sulfate (SDS) on the conformation of the following proteins were tested: lysozyme, the mitogens fromPhytolacca americana (fractions Pa2 and Pa4), lectin fromWistaria floribunda, ovine lutropin, a Bence Jones protein, and histone H2B. While the helix content of lysozyme was raised by SDS slightly, in the Bence Jones protein andW. floribunda lectin it increased from near zero to about 25–30%. In histone H2B the helix content was raised by SDS even to about 48%. However, no clear indication of helix formation could be observed in the mitogens and lutropin, even at low pH or 2.0–2.5. The tertiary structure of the proteins was perturbed by SDS. It was concluded that the reorganization of secondary structure of the proteins was favored by the following factors: (1) presence of helicogenic amino acid sequences in the protein, (2) availability of positively charged sites of the basic amino acids for interactions with the dodecyl ion, (3) absence of a large surplus of negatively charged sites on the surface of protein, and (4) absence of extensive disulfide cross-linking within the macromolecule. Both hydrophobic and electrostatic interactions occur in reconstructive denaturation, and the newly formed helices are stabilized by hydrophobic shielding by the alkyl chains of the alkyl sulfate.     

Restriction fragment length polymorphisms of horse class II MHC genes observed using various human alpha-and beta-chain cDNA probes

Genomic DNA isolated from 20 horses was digested with up to six restriction endonucleases and subjected to southern blot hybridization analysis using various human class II alpha- and beta-chain cDNA probes. A high degree of restriction fragment length polymorphism (RFLP) was found for the DQ alpha, DP beta, DQ beta and DR beta probes, about 20 polymorphic bands being detected for each. DR alpha showed 2-4 polymorphic bands, whereas no evidence for DP alpha-like genes was found. A number of correlations of RFLPs with individual alloantisera were apparent.     

Parameter estimation for the distribution of single cell lag times

In Quantitative Microbial Risk Assessment, it is vital to understand how lag times of individual cells are distributed over a bacterial population. Such identified distributions can be used to predict the time by which, in a growth-supporting environment, a few pathogenic cells can multiply to a poisoning concentration level.We model the lag time of a single cell, inoculated into a new environment, by the delay of the growth function characterizing the generated subpopulation. We introduce an easy-to-implement procedure, based on the method of moments, to estimate the parameters of the distribution of single cell lag times. The advantage of the method is especially apparent for cases where the initial number of cells is small and random, and the culture is detectable only in the exponential growth phase.     

Distinguishing Drift and Selection Empirically: “The Great Snail Debate” of the 1950s

Biologists and philosophers have been extremely pessimistic about the possibility of demonstrating random drift in nature, particularly when it comes to distinguishing random drift from natural selection. However, examination of a historical case – Maxime Lamotte’s study of natural populations of the land snail, Cepaea nemoralis in the 1950s – shows that while some pessimism is warranted, it has been overstated. Indeed, by describing a unique signature for drift and showing that this signature obtained in the populations under study, Lamotte was able to make a good case for a significant role for␣drift. It may be difficult to disentangle the causes of drift and selection acting in a population, but it is not (always) impossible.     

Melanocortin‐1 receptor structure and functional regulation

The melanogenic actions of the melanocortins are mediated by the melanocortin‐1 receptor (MC1R). MC1R is a member of the G‐protein‐coupled receptors (GPCR) superfamily expressed in cutaneous and hair follicle melanocytes. Activation of MC1R by adrenocorticotrophin or α‐melanocyte stimulating hormone is positively coupled to the cAMP signaling pathway and leads to a stimulation of melanogenesis and a switch from the synthesis of pheomelanins to the production of eumelanic pigments. The functional behavior of the MC1R agrees with emerging concepts in GPCR signaling including dimerization, coupling to more than one signaling pathway and a high agonist‐independent constitutive activity accounting for inverse agonism phenomena. In addition, MC1R displays unique properties such as an unusually high number of natural variants often associated with clearly visible phenotypes and the occurrence of endogenous peptide antagonists. Therefore MC1R is an ideal model to study GPCR function. Here we review our current knowledge of MC1R structure and function, with emphasis on information gathered from the analysis of natural variants. We also discuss recent data on the regulation of MC1R function by paracrine and endocrine factors and by external stimuli such as ultraviolet light.     

Ultrastructure of the developing pigment strand of rice (Oryza sativa L.) in relation to its role in solute transport

Summary The developing pigment strand of rice (Oryza sativa L.) was studied by conventional electron microscopy and also by use of thick sections post-fixed with zinc iodide and osmium (ZIO).When the rice caryopsis achieves maximum length, a suberised adcrusting wall layer is laid down over the original primary walls of the pigment strand. Concomitant with suberin deposition a proliferation of tubular endoplasmic reticulum occurs in the cytoplasm giving rise to numerous interconnected vesicles which bear ribosomes. The vesicles in the general cytoplasm retain their ribosomes while those close to the wall become smooth and contain an electron-opaque granular material which is eventually deposited to the outside of the plasmalemma. This granular material may be the precursor(s) from which suberin is polymerised. The suberised wall attains about six times the width of the original primary wall and plasmodesmata, which traverse both primary wall and suberised wall layers, become greatly elongated.Lipid bodies increase in both size and frequency during development, eventually coalescing to form a complete plug across the pigment strand and occluding the symplast of this tissue. The significance of these ultrastructural observations is discussed in relation to the previously demonstrated role of the pigment strand as a translocation pathway for water and assimilates during grain filling.Abbreviations ER endoplasmic reticulum - ZIO zinc iodide-osmium fixation     

The production of different morphs by alate viviparae of the aphid Myzus persicae temporarily exposed to long scotophases

The development of alatae of the green peach aphid, Myzus persicae, as gynoparae rather than as virginoparae was investigated with regard to the number of exposures to a long-night (LN) regime of 15 h darkness per diem which the aphids experienced before and/or after their birth. The minimum number of exposures to LN that resulted in all of the alatae developing into gynoparae was two prenatal plus one postnatal or one prenatal plus two postnatal, provided the scotophases in these treatments were at least 12 h long. A cumulative effect of several successive exposures to LN was also evident when the presumptive alatae were exposed to LN either from birth or not until several days after birth. Fewer exposures to LN were needed in the former case.

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Zusammenfassung Die Entwicklung von Alatae der grünen Pfirsichblattlaus, Myzus persicae, hauptsächlich zu Gynoparae, eher als zu Virginoparae, wurde im Hinblick auf den Einfluss der Anzahl an Langnächten (LN: 15 Studen Dunkelheit pro Tag), denen die Aphiden vor und/oder nach der Geburt ausgesetzt waren, untersucht. Zur ausschliesslichen Entwicklung aller Alatae zu Gynoparae waren mindestens 2 prenatale und eine postnatale LN-Exposition oder eine prenatale und 2 postnatale LN-Expositionen notwendig, vorausgesetzt die Dunkelphasen betrugen mindestens 12 Stunden. Ausserdem zeigte sich ein kumulativer Effect durch mehrere, aufeinanderfolgende LN-Expositionen, wenn die Alatae diesen von Geburt an, oder einige Tage nach der Geburt, ausgesetzt waren. Im ersten Fall waren weniger LN-Expositionen notwendig.

     

Protein polymorphism in a feral population of the pigeon Columba livia domestica

Sixteen enzymatic and non-enzymatic proteins of the pigeon Columba livia domestica were examined electrophoretically. These proteins were presumed to be under control by 22 loci. Of the 22 loci, 6 were defined as polymorphic and 15 as monomorphic. Another locus was variable, but the variation was not genetically interpretable. Average heterozygosity calculated over 21 loci was 0.075.     

A new lipoprotein allotype Lprs and allele Lpr1,3 in the pig

Specific alloprecipitins were found in blood plasma of pigs, immunized by sera of Lpr1 positive donors. These precipitins detected a new allotype of the lipoprotein Lpr system which was designated Lpr3. Genetic studies confirmed its codominant inheritance and subgroup character. This linear subgroup of allotype Lprl is controlled by the allele Lpr^1,3. Investigations in populations of 14 pig breeds showed significant interbreed differences in the frequencies of alleles Lpr¹, Lpr² and Lpr^1,3.     

Angiotensin converting enzyme gene polymorphism studies: A case-control study

Mild gestational hyperglycemia (MGH) is a very common complication of pregnancy that is characterized by intolerance to glucose. The association of angiotensin-converting enzyme (ACE) insertion/deletion (I/D) polymorphism to MGH has been previously reported. In this study, we evaluated the association between ACE polymorphism and the risk of MGH in a Saudi population. We conducted a case-control study in a population of 100 MGH patients and 100 control subjects. ACE gene polymorphism was analyzed by the novel approach of tetraprimer amplification refractory mutation system (ARMS)-polymerase chain reaction (PCR). The frequency of ACE polymorphism was not associated with either alleles or genotypes in MGH patients. Glucose concentration was found to be significantly associated with the MGH group. Our study suggests that ACE genotypes were not associated with ACE polymorphism in a Saudi population.