Molecular dynamics model of unliganded HIV-1 reverse transcriptase

HIV-1 RT is one of the most important antiviral targets in the treatment of acquired immunodeficiency syndrome (AIDS). Several crystallographic structures are available for this enzyme, mostly with bound inhibitors. Despite their importance for structure based drug design towards new anti-HIV retrovirals, the X-ray structures of the unliganded enzyme could only be obtained incomplete, with a low resolution and until recently even the conformation of the p66 thumb was controversial. In this work we have aligned different X-ray RT structures, and built up a computational model of RT using homology modeling, which was afterwards refined and validated through MD simulations with explicit solvent. The model enzyme was structurally stable through the whole MD simulation, showing a RMSD of 2 Angstrom from the starting geometry. The Ramanchandram plot has improved along the simulation. Both intra-domain and interdomain movements were observed. The thumb kept its closed conformation through the whole simulation. A contact map, hydration sites study and a detailed analysis of the solvation of the nucleotide binding site are also presented.

The Carboxylate Shift in Zinc Enzymes: A Computational Study

Zinc is the second most abundant transition element in biology and the only metal known to be represented in enzymes from each one of the six classes established by the International Union of Biochemistry. The flexible coordination geometry, the fast ligand exchange, the lack of redox activity, and its role as Lewis acid are just some of the features that make zinc an invaluable element in biological catalysis. In this study, we have analyzed the importance in mononuclear Zn enzymes of an interesting mechanistic phenomenon known as carboxylate shift, which is characterized by a change in the coordination mode of a carboxylate group (mono to bidentate or vice versa) with both ligand entrance or exit from the metal coordination sphere. Using B3LYP calculations, we were able to unveil in detail patterns relating the intrinsic characteristics of a given Zn coordination sphere with the existence or not of a carboxylate-shift mechanism and the additional energy stabilization arising from it. In particular, a specific Zn coordination sphere containing a carboxylate ligand (Asp or Glu), a cysteine, and a histidine has been shown to have the most favorable combination of amino acid residues that ensures a fast ligand exchange.

Comparative evolutionary genomics of the HADH2 gene encoding Abeta-binding alcohol dehydrogenase/17beta-hydroxysteroid dehydrogenase type 10 (ABAD/HSD10)

Background

The Aβ-binding alcohol dehydrogenase/17β-hydroxysteroid dehydrogenase type 10 (ABAD/HSD10) is an enzyme involved in pivotal metabolic processes and in the mitochondrial dysfunction seen in the Alzheimer's disease. Here we use comparative genomic analyses to study the evolution of the HADH2 gene encoding ABAD/HSD10 across several eukaryotic species.

Results

Both vertebrate and nematode HADH2 genes showed a six-exon/five-intron organization while those of the insects had a reduced and varied number of exons (two to three). Eutherian mammal HADH2 genes revealed some highly conserved noncoding regions, which may indicate the presence of functional elements, namely in the upstream region about 1 kb of the transcription start site and in the first part of intron 1. These regions were also conserved between Tetraodon and Fugu fishes. We identified a conserved alternative splicing event between human and dog, which have a nine amino acid deletion, causing the removal of the strand β_F. This strand is one of the seven strands that compose the core β-sheet of the Rossman fold dinucleotide-binding motif characteristic of the short chain dehydrogenase/reductase (SDR) family members. However, the fact that the substrate binding cleft residues are retained and the existence of a shared variant between human and dog suggest that it might be functional. Molecular adaptation analyses across eutherian mammal orthologues revealed the existence of sites under positive selection, some of which being localized in the substrate-binding cleft and in the insertion 1 region on loop D (an important region for the Aβ-binding to the enzyme). Interestingly, a higher than expected number of nonsynonymous substitutions were observed between human/chimpanzee and orangutan, with six out of the seven amino acid replacements being under molecular adaptation (including three in loop D and one in the substrate binding loop).

Conclusion

Our study revealed that HADH2 genes maintained a reasonable conserved organization across a large evolutionary distance. The conserved noncoding regions identified among mammals and between pufferfishes, the evidence of an alternative splicing variant conserved between human and dog, and the detection of positive selection across eutherian mammals, may be of importance for further research on ABAD/HSD10 function and its implication in the Alzheimer's disease.

Molecular insights into the mechanisms of HIV-1 reverse transcriptase resistance to nucleoside analogs

The causative agent of acquired immunodeficiency syndrome, HIV-1, depends on one of its enzymes, reverse transcriptase, to copy its single stranded RNA genome into a double stranded DNA nucleic acid suitable for integration in the host cell genome. In the last two decades, the advances in the knowledge of the kinetic mechanism of reverse transcription and in the determination of the crystallographic structures for the complexes of the enzyme with substrates and products were huge. However, all of this knowledge resulted in the design of RT inhibitors for which the virus, after a short period of exposure, becomes less susceptible, due to the development of resistance. The development of resistance is caused by the high frequency of viral mutation and the toxicity of those same drugs. Therefore, a closer look at all the available information might shed some light into this subject and help to develop new strategies to overcome the lack of long term clinical efficiency of these drugs. Here, we present a critical atomic level study of all the mutations that have been detected and reported so far, as a reaction of the enzyme to counteract the action of the inhibitors.

Detailed microscopic study of the full zipA:FtsZ interface

Protein-protein interaction networks are very important for a wide range of biological processes. Crystallographic structures and mutational studies have generated a large number of information that allowed the discovery of energetically important determinants of specificity at intermolecular protein interfaces and the understanding of the structural and energetic characteristics of the binding hot spots. In this study we have used the improved MMPB/SA (molecular mechanics/Poisson-Boltzmann surface area) approach that combining molecular mechanics and continuum solvent permits to calculate the free energy differences upon alanine mutation. For a better understanding of the binding determinants of the complex formed between the FtsZ fragment and ZipA we extended the alanine scanning mutagenesis study to all interfacial residues of this complex. As a result, we present new mutations that allowed the discovery of residues for which the binding free energy differences upon alanine mutation are higher than 2.0 kcal/mol. We also observed the formation of a hydrophobic pocket with a high warm spot spatial complementarity between FtsZ and ZipA. Small molecules could be designed to bind to these amino acid residues hindering the binding of FtsZ to ZipA. Hence, these mutational data can be used to design new drugs to control more efficiently bacterial infections.

Unraveling the Importance of Protein−Protein Interaction: Application of a Computational Alanine-Scanning Mutagenesis to the Study of the IgG1 Streptococcal Protein G (C2 Fragment) Complex

Alanine-scanning mutagenesis of protein-protein interfacial residues is a very important process for rational drug design. In this study, we have used the improved MM-PBSA approach that combining molecular mechanics and continuum solvent permits one to calculate the free energy differences through alanine mutation. To identify the binding determinants of the complex formed between the IgG1 (immunoglobulin-binding protein G) and protein G, we have extended the experimental alanine scanning mutagenesis study to both proteins of this complex and, therefore, to all interfacial residues of this binding complex. As a result, we present new residues that can be characterized as warm spots and, therefore, are important for complex formation. We have further increased the understanding of the functionality of this improved computational alanine-scanning mutagenesis approach testing its sensitivity to a protein-protein complex with an interface made up of residues mainly polar. In this study, we also have improved the method for the detection of an important amino acid residue that frequently constitutes a hot spot--tryptophan.

Theoretical Study of the Unusual Protonation Properties of the Active Site Cysteines in Thioredoxin

The thiol/disulfide oxidoreductases of the thioredoxin family have, in the active site, two cysteines that can be in a reduced or an oxidized form. One of the cysteines in the reduced state is deprotonated, and it is called nucleophilic cysteine. The pK(a) of this cysteine is different from that of a normal cysteine and varies widely among the different enzymes of this family. However, the factors responsible for the different degrees of stabilization of nucleophilic cysteine thiolate are not fully understood. Here, we have studied the well-known hypothesis of proton sharing between the active site thiols by performing a linear transit scan for the transfer of the proton between the active site cysteines. We used a two-layered (DFT/MM) ONIOM formalism, with the active site region treated at the B3LYP/6-31+G(d) level and the remains of the protein treated with the Amber Parm94 force field. The solvation free energy was accounted for with a continuum solvent model, by solving the Poisson-Boltzmann equation using the program Delphi. We have obtained excellent agreement with the experimental data available in the literature. Besides refuting the proton sharing hypothesis, our results include a value of 14.0 for the pK(a) of the buried cysteine, a quantity that has not been possible to obtain experimentally but which has been proven to be higher than 11. Additionally, this study also provides detailed information on the very interesting and so far unknown fact that the contribution of the enzymatic structure (8.3 kcal/mol) prevails in relation to that of the solvent (0.60 kcal/mol) concerning the differential stabilization of the active site thiolates.

Determination of the ΔpKa between the active site cysteines of thioredoxin and DsbA

Thioredoxin superfamily members share a considerable degree of structural similarity, with a conserved CX(i)X(j)C motif at the active site, where C stand for two cysteines that alternate between a reduced thiol and oxidized disulfide states, and X(i)and X(j) are two amino acids different in each family member. Despite these similarities, they display very different redox potentials and pKas for the active site dithiol, and fulfill different physiological roles. Thioredoxin, for example, promotes the reduction of disulfide bonds, while DsbA promotes their oxidation in prokaryotic cells. The factors that promote these differences are still not fully understood. However, it is generally accepted that the different stabilities of the redox active disulfide bond depends on the degree of stabilization, in the reduced state, of the thiolate of one of the active site cysteines (nucleophilic cysteine). In this work we have used QM/MM methods to compare and characterize the active site dithiols of both enzymes, and to shed some light on the structural features responsible for the large differences in pKa and redox potential between two homologous enzymes, thioredoxin and DsbA. We have also analyzed the main factors pointed out in the literature as responsible for their different properties. We obtained the value of 4.5 for pKa difference (DeltapKa) between the nucleophilic cysteines of both enzymes, which is in excellent agreement with most of the experimental values. Additionally, we found that the principal differentiating factor responsible for this observed DeltapKa are the alpha2-alpha helices, which greatly contribute to the mentioned value, by stabilizing the DsbA thiolate in a much greater extend than the thioredoxin thiolate. A double mutation of the conserved residues Asp26 and Lys57, in thioredoxin, and Glu24 Lys58, in DsbA, by alanines did not change the DeltapKa value; this supports the hypothesis that these residues are not involved in the differentiation of the properties of the active centre dithiol. However, we found out that these residues are important for the stabilization of the nucleophilic thiolate. The X(i) and X(j) residues also do not seem to promote the stabilization of the thiolates. In fact, the corresponding double alanine mutants are more stable than the wild-type enzymes. However, these residues are involved in the differentiation between thioredoxin and DsbA, stabilizing the DsbA thiolate by a larger extent than the thioredoxin thiolate.

Overview of ribonucleotide reductase inhibitors: an appealing target in anti-tumour therapy

This review provides up-to-date information on the inhibition of ribonucleotide reductase (RNR), the enzyme that catalyses the reduction of ribonucleotides into deoxyribonucleotides. Taking in account that DNA replication and repair are essential mechanisms for cell integrity and are dependent on the availability of deoxyribonucleotides, many researchers are giving special attention to this enzyme, since it is an attractive target to treat several diseases of our time specially cancer. This investment has already given some benefits since some of these inhibitors show potent chemotherapeutic efficacy against a wide range of tumours such as non-small cell lung cancer, adenocarcinoma of pancreas, bladder cancer, leukaemia and some solid tumours. In fact a few of them have already been approved for the clinical treatment of some kinds of cancer. All aspects of RNR inhibition and corresponding inhibitors are the subjects of this review. The inhibitors are divided in three main groups: translation inhibitors, which unable the formation of the enzyme; dimerization inhibitors that prevent the complexation of the two RNR subunits (R1 and R2); and catalytic inhibitors that inactivate subunit R1 and/or subunit R2, leading to RNR inactivity. In this last group special focus will be addressed to substrate analogues.

Similarities and differences in the thioredoxin superfamily

There is growing interest in the proteins involved in protein folding. This is mainly due to the large number of human diseases related to defects in folding, which include cystic fibrosis, Alzheimer's and cancer. However, equally important as the oxidation and concomitant formation of disulfide bridges of the extracellular or secretory proteins is the reduction and maintenance in the reduced state of the proteins within the cell. Interestingly, the proteins that are responsible for maintenance of the reduced state belong to the same superfamily as those responsible for the formation of disulfide bridges: all are members of the thioredoxin superfamily. In this article, we highlight the main features of those thioredoxin-like proteins directly involved in the redox reactions. We describe their biological functions, cytoplasmic location, mechanisms of action, structures and active site features, and discuss the principal hypotheses concerning origins of the different reduction potentials and unusual pK(a)'s of the catalytic residues.

Farnesyltransferase--new insights into the zinc-coordination sphere paradigm: evidence for a carboxylate-shift mechanism

Despite the enormous interest that has been devoted to the study of farnesyltransferase, many questions concerning its catalytic mechanism remain unanswered. In particular, several doubts exist on the structure of the active-site zinc coordination sphere, more precisely on the nature of the fourth ligand, which is displaced during the catalytic reaction by a peptide thiolate. From available crystallographic structures, and mainly from x-ray absorption fine structure data, two possible alternatives emerge: a tightly zinc-bound water molecule or an almost symmetrical bidentate aspartate residue (Asp-297beta). In this study, high-level theoretical calculations, with different-sized active site models, were used to elucidate this aspect. Our results demonstrate that both coordination alternatives lie in a notably close energetic proximity, even though the bidentate hypothesis has a somewhat lower energy. The Gibbs reaction and activation energies for the mono-bidentate conversion, as well as the structure for the corresponding transition state, were also determined. Globally, these results indicate that at room temperature the mono-bidentate conversion is reversible and very fast, and that probably both states exist in equilibrium, which suggests that a carboxylate-shift mechanism may have a key role in the farnesylation process by assisting the coordination/displacement of ligands to the zinc ion, thereby controlling the enzyme activity. Based on this equilibrium hypothesis, an explanation for the existing contradictions between the crystallographic and x-ray absorption fine structure results is proposed.

New designs for MRI contrast agents

New designs for Magnetic Resonance Imaging contrast agents are presented. Essentially, they all are host-guest inclusion complexes between y-cyclodextrins and polyazamacrocycles of gadolinium (III) ion. Substitutions have been made to the host to optimise the host-guest association. Molecular mechanics calculations have been performed, using the UFF force field for metals, to decide on the suitability of the substitutions, and to evaluate the host-guest energies of association. Interesting general conclusions have been obtained, concerning the improvement of Magnetic Resonance Imaging contrast agents; namely, a set of rational methodologies have been deduced to improve the association between the gadolinium (III) chelates and the cyclodextrins, and their efficiency is demonstrated with a large set of substituted complexes, opening new doors to increase the diagnostic capabilities of Magnetic Resonance Imaging.

The contribution of mild thiamine deficiency and ethanol consumption to central cholinergic parameter dysfunction and rats' open-field performance impairment

We studied at the biochemical, morphological, and behavioral levels the effect of chronic ethanol consumption, associated or not with a mild thiamine deficiency episode. We found that (i) thiamine deficiency induced a significant decrease of the acetylcholinesterase (AChE) activity both in cortex and hippocampus; (ii) chronic ethanol treatment has no effect on cortical AChE activity, but induced a significant decrease of hippocampal enzyme activity; (iii) the reduction in cortical and hippocampal AChE activity induced by chronic ethanol treatment associated with a 1-week thiamine deficiency was also significant and was greater than that induced by ethanol alone. Furthermore, either chronic ethanol or thiamine deficiency induced a significant decrease in the release of acetylcholine (ACh) in the stimulated condition using high potassium concentration; and when both treatments were associated the decrease was even greater. In the unstimulated condition, the reduction in the release of ACh was greater for ethanol treatment than for thiamine deficiency. Open-field tests showed that only in the "sniffing" category were there significant differences among the experimental groups. No morphological change was detected by optical microscopy, suggesting that the injury process was in its initial stages in which only functional and behavioral changes are displayed. In addition, our biochemical results indicate that cortical cholinergic susceptibilities to ethanol and thiamine deficiency are significantly different.

Flocculation of Saccharomyces cerevisiae is induced by transformation with the GAP1 gene from Kluyveromyces marxianus

A non-flocculent strain of Saccharomyces cerevisiae was transformed with the GAP1 gene which encodes p37, a GAPDH-like protein present in the cell wall of Kluyveromyces marxianus flocculent cells. The transformed cells were characterized with respect to flocculation behaviour, morphology, growth, cell wall integrity and GAPDH activity. A flocculent phenotype was acquired by the transformed cells, showing a behaviour in respect to flocculation/deflocculation very similar to that of K. marxianus. The presence of p37 in the cell wall was assessed by immunoprecipitation of biotinylated cell wall proteins and an accumulation of p37 was evident in the cell wall of transformed cells. This result was confirmed by studies using a chimeric protein resulting from fusing the p37 with a yeast-enhanced green fluorescent protein, yEGFP. The recombinant protein was localized mainly in the cell wall of the transformed strain, although the presence of p37 in the cytosol was indicated by an increase in GAPDH activity. Calcofluor white sensitivity tests indicated that the cell wall structure is affected by the accumulation of p37. These results provided further evidence of p37 function regarding flocculation and that although lacking a N-terminal signal peptide p37 is targeted to the cell wall.

Effect of parity on pituitary prolactin response to metoclopramide and domperidone: implications for the enhancement of lactation

OBJECTIVE

The gastrointestinal motility agents metoclopramide and domperidone are known to increase pituitary prolactin (PRL) secretion and breast milk production. This study compared the effect of single doses of two strengths of metoclopramide and a single dose of domperidone on PRL secretion.

METHODS

Ten nonpregnant women had baseline evaluation of serum PRL concentrations. The PRL concentrations were then determined after random oral administration of metoclopramide 10 mg, metoclopramide 5 mg, and domperidone 10 mg. Blood samples were drawn in the first 7 days of the menstrual cycle, at 13 time points over a 6-hour period (0, 15, 30, 45, 60, 75, 90, 120, 150, 180, 240, 300, and 360 minutes), with the zero time point beginning at 0800 hours. Variables such as weight, height, age, gravidity, parity, and oral contraceptive use were recorded.

RESULTS

Baseline PRL concentrations showed the natural circadian rhythm. Metoclopramide and domperidone both caused a significant increase in PRL. However, PRL secretion was most influenced by parity. Nulliparous women had the quickest and highest PRL secretion with metoclopramide 10 mg, compared with the PRL response with metoclopramide 5 mg and domperidone 10 mg. Conversely, multiparous women had PRL secretion patterns that were equivalent between the medications.

CONCLUSIONS

The PRL response to the medications was most influenced by parity. Therefore, we suggest that the medication therapy of choice for enhancing lactation may not be the same in all women, but may instead be determined by parity.

The acute release of maternal prolactin by instrumental cervical dilatation simulates the second stage of labor

OBJECTIVE

We hypothesize that artificial stimulation of the cervix causes an acute secretion of maternal prolactin (PRL) that mimics PRL secretion during the second stage of human labor.

METHODS

Eighteen women scheduled for first-trimester therapeutic abortion had a blood sample drawn at the following times: before and after laminaria tent (LT) insertion for cervical ripening, 18-24 hours later upon entry in the procedure room, after LT removal, during instrumental cervical dilatation and uterine evacuation by suction curretage, soon after evacuation, and 1/2 hour and 1 hour after evacuation. Local cervical anesthesia, intravenous analgesics, and sedation were administered before the procedure. Blood serum was assayed for PRL, human chorionic gonadotropin (hCG), and estradiol.

RESULTS

The initial PRL levels were 34 ng/mL +/- 4.2 standard error of the mean (SEM) and did not change after 18-24 hours of LT placement nor after LT removal. However, PRL increased significantly (t = 5.8; P = .00001) over basal levels by 204% +/- 15 at the time of instrumental dilatation and rose to 378% +/- 33 at 1/2 hour postevacuation. After 1 hour, PRL had declined to 173% +/- 10%. Serum levels of estradiol and hCG changed only after evacuation.

CONCLUSION

Artificial stimulation of the cervix causes an immediate surge in PRL levels. We suggest that the acute increase in pituitary PRL secretion that occurs during the second stage of labor results from a neural signal from the cervix and not from endocrine changes associated with labor.

Kluyveromyces marxianus flocculence and growth at high temperature is dependent on the presence of the protein p37

A Kluyveromyces marxianus mutant deficient in p37, a glyceraldehyde-3-phosphate dehydrogenase (GAPDH)-like protein, was obtained and characterized with respect to flocculation behaviour, resistance to temperatures above the optimum for growth, morphology, growth, calcofluor white sensitivity and GAPDH activity. In YPD media, the mutant cells were unable to flocculate and were thermosensitive. However, this thermosensitivity could be overcome by the presence of calcium. Calcofluor white was toxic to the mutant, indicating that the mutation affects cell wall structure. The contribution of p37 to total GAPDH activity was 25% when cells were using glucose as carbon source and 50% when cells were growing in 3% ethanol. These results indicate that p37 is likely to be involved in thermotolerance and flocculation, which can be related to its contribution to cell wall integrity.

Maternal prolactin secretion is phasic during induced term and post-term labor

OBJECTIVE

We hypothesized that regimens of labor induction do not alter the biphasic secretion of maternal prolactin (PRL) seen during spontaneous labor.

METHODS

Serial blood samples drawn from 12 women before, during, and after induced labor were assayed for PRL and hCG and compared with cervical dilatation and uterine contraction frequency (UCF). Induction methods were cervical ripening with dinoprostone gel (Prepidil) followed by oxytocin infusion (n = 1), amniotomy followed by oxytocin (n = 4), oxytocin followed by amniotomy (n = 3), amniotomy only (n = 2), and oxytocin only (n = 2).

RESULTS

Regardless of the induction method, PRL decreased with advancing cervical dilatation during the first stage of labor and reached a nadir at full dilatation. Prolactin levels then increased rapidly during the second stage, correlating significantly with the increase in UCF, and peaked at 1 hour postpartum before decreasing. Levels of hCG increased during labor and peaked just before or at delivery before rapidly decreasing.

CONCLUSIONS

The biphasic secretion of maternal PRL is a fundamental characteristic of active term labor and occurs regardless of the method used to induce labor.

Phasic maternal prolactin secretion during spontaneous labor is associated with cervical dilatation and second-stage uterine activity

OBJECTIVE

In this study, we attempted to determine the physiologic roles of prolactin (PRL) and hCG during labor.

METHODS

Serial blood samples were collected from 19 women (15 multiparous and four nulliparous) before, during, and after labor; assayed for PRL and hCG; and compared with cervical dilatation and uterine contraction frequency.

RESULTS

Prolactin levels decreased in association with progressive cervical dilatation during the first stage of labor and reached a nadir at full dilatation. Thereafter, PRL increased rapidly during the second stage of labor and peaked within 1 hour postpartum. Uterine contraction frequency also increased during the second stage and correlated significantly (r2 = 0.60; P = .0006) with levels of PRL. Levels of hCG increased during labor and peaked at about the time of delivery.

CONCLUSION

These data suggest that phasic PRL secretion is associated with cervical dilatation and that after transition to the second stage of labor, uterine contraction frequency may be associated with the increase in PRL levels.

Characterization of the glyceraldehyde-3-phosphate dehydrogenase gene family from Kluyveromyces marxianus--polymerase chain reaction-single-strand conformation polymorphism as a tool for the study of multigenic families

Three glyceraldehyde-3-phosphate dehydrogenase (GAPDH) genes from Kluyveromyces marxianus were identified and characterized. The coding region of two of them (GAP2 and GAP3) is very similar (99.6% homology). The other gene (GAP1) is only 86% homologous to GAP2 or GAP3 and is responsible for the expression of Gap1p. This protein is extremely homologous to the K. marxianus cell wall protein p37, presumably involved in flocculation. However, no leader sequence could be detected in this gene. The identification of the three genes was possible with the use of polymerase chain reaction-single-strand conformation polymorphism (PCR-SSCP), as it permits us to overcome the difficulties caused by the high homology amongst the genes. Expression of the GAPDH genes under different carbon sources (glucose or ethanol) was assessed either by Northern blot or reverse transcription-PCR-SSCP analysis, revealing that genes GAP1 and GAP2, but not GAP3, are transcribed. The results also indicate that the transcription of the gene encoding the cell wall protein p37 (Gap1p) is not dependent on the carbon source, in contrast with the expression of the gene GAP2, which is affected in cells growing in a glucose-depleted medium.

Y body association with morphologic heterogeneity of human sperm

OBJECTIVE

The purpose of this study was to determine a possible association between the Y body and sperm head shape, since sperm head shape may be a factor that influences the rate of migration of X- and Y-bearing sperm cells.

MATERIALS

Sperm cell (n = 1,065) preparations from seven donors were fluorochrome stained for the Y body, and area and shape of Y body-positive and -negative cells were measured from digitized images. The distributions of the segregated cell population measurements were statistically analyzed nonparametrically.

RESULTS

Of the total cells, 528 were Y body-positive and 537 were not, and the ratio (0.983) of the two cell categories, both within and between donors, was equivalent to the theoretical ratio of 1.0 expected for the X:Y sperm cell population. Sperm head area distributions were equal between the two populations. However, the length-width ratios of Y-bearing cells were significantly higher (P < .0001) and calculated roundness was significantly (P = .006) less than non Y body-bearing cells.

CONCLUSIONS

The Y body may represent the Y chromosome. Furthermore, the Y body may impart a more ellipsoidal shape to sperm cells. Sperm shape may influence the migration rate of cells through cervical mucus such that differences in the male-to-female sex ratio of conceptuses, and at birth, may reflect a shape-imparted advantage in the migration rate of Y-bearing sperm in reaching the oocyte.

Flocculation of Kluyveromyces marxianus is induced by a temperature upshift

An upshift of the growth temperature from 26 to 40 degrees C in the presence of calcium leads to the aggregation of Kluyveromyces marxianus cells and to the formation of flocs. Analysis of cell wall proteins, either by sodium dodecyl sulphate-polyacrylamide gel electrophoresis of extractable mannoproteins or by immunolocalization, revealed an accumulation of a protein with Mr 37 kDa(p37), upon flocculation. Immunological studies confirmed the homology of this protein with the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH). When mRNA isolated from cells growing at 40 degrees C was translated in vitro, a 35 kDa newly labelled protein was synthesized and immunoprecipitation assays showed that this protein is recognized by p37-antiserum, suggesting that the 35 kDa polypeptide might be an unglycosylated precursor for of p37. The results indicated that the presence of this cell wall mannoprotein closely related to GAPDH is dependent on the growth temperature, suggesting its role as adhesin.

A protein homologous to glyceraldehyde-3-phosphate dehydrogenase is induced in the cell wall of a flocculent Kluyveromyces marxianus

A protein with an apparent molecular weight of 37,000 (p37) is present in very large amounts in the cell wall of Kluyveromyces marxianus, after the induction of flocculation of the yeast. This protein was isolated by preparative gel electrophoresis and its purity checked by SDS-PAGE and reverse-phase HPLC. SDS-PAGE, endoglycosidase-H treatment and peptide sequencing indicated that p37 is a glycoprotein with a high identity to cytosolic glyceraldehyde-3-phosphate dehydrogenase from Saccharomyces cerevisiae. Polyclonal antibodies were used for Western blot analysis and immunocytochemistry, which showed that p37 is present in the cell wall of non-flocculent K. marxianus and, therefore, is a constitutive protein of the cell wall.

Quantitative analysis of the effect of freezing on donor sperm motion kinetics

One hundred ninety-two semen specimens from 14 donors were analyzed on a CellSoft Semen Analyzer (CRYO Resources, New York, NY) before and after freezing. Mean post-thaw motility decreased by 52%. Correlation of the percent decrease in post-thaw versus prefreeze motility was significant but of poor predictive value. Comparisons of the percent change in post-thaw motility and sperm motion kinetics between four discrete ranges of prefreeze motility (32% to 66%, 67% to 76%, 77% to 84%, 85% to 94%) revealed that the effect of freezing on sperm cell survival was equivalent between all ranges. However, significant differences occurred between these ranges for curvilinear velocity, straight line velocity, and mean amplitude of lateral head displacement but not for linearity nor beat cross frequency. All correlations between prefreeze and post-thaw motion variables were significant but closest for curvilinear velocity and straight line velocity. Furthermore, correlations of prefreeze versus post-thaw velocity measurements were strongest for those cells within the 65% to 85% range of prefreeze motility. We suggest that sperm survival is independent of prefreeze motility. However, velocity kinetics appear stable after freezing for those specimens that had an initial motility of 65% to 85%.

Concentration of receptors for estradiol and progesterone in canine endometrium during estrus and diestrus

Receptors for estrogen and progesterone were measured in cytosols prepared from specimens of canine endometrium obtained at late proestrus, day 4 of estrus, day 2 of diestrus, and at 10 day intervals from days 10 through 80 of diestrus. Twenty nine adult bitches were used, with 2 to 4 dogs used at each time point. Concentrations of estradiol receptors measured in endometrial cytosols from late proestrus through day 10 of diestrus were similar (mean +/- SEM: 9.9 +/- 2.2, 10.5 +/- 1.2, 16.3 +/- 1.6, and 16.2 +/- 2.9 pmol/g of tissue at proestrus, day 4 of estrus, days 2 and 10 of diestrus, respectively). As serum concentrations of progesterone increased during early diestrus, the concentration of estradiol receptors decreased and were significantly (P less than 0.05) lower on days 30 (4.9 +/- 1.3 pmol/g of tissue) and 40 (3.7 +/- 0.6 pmol/g of tissue) of diestrus. After day 40 of diestrus, when serum concentrations of progesterone were approaching basal concentrations, the concentration of estradiol receptors increased and remained significantly (P less than 0.05) higher from days 60 to 80 of diestrus (day 60, 13.4 +/- 2.9; day 70, 15.7 +/- 1.7; day 80, 19.8 +/- 2.4 pmol/g of tissue). As observed for estrogen receptors, the concentration of endometrial receptors for progesterone also gradually increased from late proestrus (4.9 +/- 1.3 pmol/g of tissue) to day 2 of diestrus (6.4 +/- 0.3 pmol/g of tissue).(ABSTRACT TRUNCATED AT 250 WORDS)

Luteal function in the bitch: changes during diestrus in pituitary concentration of and the number of luteal receptors for luteinizing hormone and prolactin

The concentration of unoccupied luteal receptors for luteinizing hormone (LH) and prolactin, and the concentration of these two hormones in the pituitary was determined in 11 groups of bitches (n = 3 or 4/group) representing stages from proestrus through Day 80 of diestrus. Despite dramatic changes in serum concentrations of progesterone, the concentration of luteal receptors for LH and prolactin was quite constant throughout the entire luteal phase. In association with the ovulatory surge of LH, pituitary concentration of LH decreased abruptly from proestrus to Day 2 of diestrus, and was then gradually replenished during the remainder of diestrus. The concentration of prolactin in the pituitary did not vary significantly from proestrus through late diestrus.