A pilot study of oral L-arginine in cystic fibrosis

Exhaled nitric oxide has previously been found to be low in cystic fibrosis. The aim of this study was to determine whether exhaled nitric oxide levels would increase in response to oral L-arginine supplementation administered daily for 4 weeks. Exhaled and nasal nitric oxide was measured weekly. Plasma L-arginine levels increased in response to supplementation but this was not reflected in an increase in eNO levels.

Ratio spectra derivative spectrophotometry for the determination of furosemide and spironolactone in a capsule formulation

The determination of furosemide and spironolactone in a capsule formulation has been investigated using techniques such as Vierordt's method and derivative spectroscopy dA/d lambda and d2A/d lambda2 applying the zero-crossing technique following reported methods. In our hands, using standard mixtures, these methods gave unreliable results. We have therefore investigated the use of ratio spectra derivative spectrophotometry for this determination. The technique of ratio spectra derivative spectrophotometry was developed in 1990, and has recently been used for a number of analyses of co-formulated products. The method was applied to the analysis of standard mixtures of the two drugs and the combined contents of 20 capsules resulting in values (mean +/- standard deviation) of 102.1 +/- 1.9% and 101.4 +/- 4.0% of the stated content for furosemide and spironolactone, respectively. Similarly, the analysis of individual capsules resulted in values of 101.5 +/- 1.6% and 102.2 +/- 1.4% of the stated content for furosemide and spironolactone, respectively.

Transcription profile of brewery yeast under fermentation conditions

AIMS

Yeast strains, used in the brewing industry, experience distinctive physiological conditions. During a brewing fermentation, yeast are exposed to anaerobic conditions, high pressure, high specific gravity and low temperatures. The purpose of this study was to examine the global gene expression profile of yeast subjected to brewing stress.

METHODS AND RESULTS

We have carried out a microarray analysis of a typical brewer's yeast during the course of an 8-day fermentation in 15 degrees P wort. We used the probes derived from Saccharomyces cerevisiae genomic DNA on the chip and RNA isolated from three stages of brewing. This analysis shows a high level of expression of genes involved in fatty acid and ergosterol biosynthesis early in fermentation. Furthermore, genes involved in respiration and mitochondrial protein synthesis also show higher levels of expression.

CONCLUSIONS

Surprisingly, we observed a complete repression of many stress response genes and genes involved in protein synthesis throughout the 8-day period compared with that at the start of fermentation.

SIGNIFICANCE AND IMPACT OF THE STUDY

This microarray data set provides an analysis of gene expression under brewing fermentation conditions. The data provide an insight into the various metabolic processes altered or activated by brewing conditions of growth. This study leads to future experiments whereby selective alterations in brewing conditions could be introduced to take advantage of the changing transcript profile to improve the quality of the brew.

Determination of yeast glycogen content by individual cell spectroscopy using image analysis

A rapid technique has been developed to determine the glycogen content of yeast on an individual cell basis using a combination of image analysis technology and staining of yeast cells with an I(2):KI solution. Changes in mean cellular glycogen content during alcoholic fermentation have been reported using this technique. The glycogen content of stored brewer's yeast is heterogeneous compared to freshly propagated yeast which have a more uniform distribution of glycogen. Analysis of the distribution of yeast glycogen during fermentation indicates that a fraction of yeast cells do not dissimilate glycogen. Therefore, conventional analysis of the mean glycogen content of yeast used to inoculate fermentations is of limited use, unless information regarding the proportion of cells which utilize glycogen is known. Analysis of the distribution of glycogen within a yeast population can serve as a useful indicator of yeast quality.

The stress response is repressed during fermentation in brewery strains of yeast

Yeast cells encounter a variety of environmental stresses during brewing and must respond to ensure cell survival. Cells can respond to stress by inducing a Heat Shock Response in which heat shock proteins (Hsps) are synthesized. In laboratory strains of Saccharomyces cerevisiae, the heat shock protein, Hsp104, plays a major role in the acquisition of tolerance to a variety of stresses such as heat, ethanol and sodium arsenite, and as such acts as an excellent stress indicator. The induction of Hsp104 in bottom-and top-fermenting brewery strains was examined when grown under laboratory and industrial fermentation conditions, and it was found that each brewing strain exhibits its own unique pattern of Hsp104 expression. During industrial fermentations, brewery strains are capable of mounting a stress response at the early stages of fermentation. However, as the fermentation proceeds, the response is repressed. The results suggest that conditions experienced in industrial brewing prevent the activation of the stress response. This study increases our understanding of alterations in gene expression patterns during the brewing process, and yields information that will aid in the definition of best practice in yeast management.

Conserved polar residues in the transmembrane domain of the human tachykinin NK2 receptor: functional roles and structural implications

We have studied the effects of agonist and antagonist binding, agonist-induced activation and agonist-induced desensitization of the human tachykinin NK2 receptor mutated at polar residues Asn-51 [in transmembrane helix 1 (TM1)], Asp-79 (TM2) and Asn-303 (TM7), which are highly conserved in the transmembrane domain in the rhodopsin family of G-protein-coupled receptors. Wild-type and mutant receptors were expressed in both COS-1 cells and Xenopus oocytes. The results show that the N51D mutation results in a receptor which, in contrast with the wild-type receptor, is desensitized by the application of a concentration of 1 microM of the partial agonist GR64349, indicating that the mutant is more sensitive to agonist activation than is the wild-type receptor. In addition, we show that, whereas the D79E mutant displayed activation properties similar to those of the wild-type receptor, the D79N and D79A mutants displayed a severely impaired ability to activate the calcium-dependent chloride current. This suggests that it is the negative charge at Asn-79, rather than the ability of this residue to hydrogen-bond, that is critical for the activity of the receptor. Interestingly, the placement of a negative charge at position 303 could compensate for the removal of the negative charge at position 79, since the double mutant D79N/N303D displayed activation properties similar to those of the wild-type receptor. This suggests that these two residues are functionally coupled, and may even be in close proximity in the three-dimensional structure of the human tachykinin NK2 receptor. A three-dimensional model of the receptor displaying this putative interaction is presented.

The relationship between the agonist-induced activation and desensitization of the human tachykinin NK2 receptor expressed in Xenopus oocytes

1. Repeated applications of neurokinin A (NKA) to oocytes injected with 25 ng wild-type hNK2 receptor cRNA caused complete attenuation of second and subsequent NKA-induced responses while analogous experiments using repeated applications of GR64349 and [Nle10]NKA(4-10) resulted in no such desensitization. This behaviour has been previously attributed to the ability of the different ligands to stabilize different active conformations of the receptor that have differing susceptibilities to receptor kinases (Nemeth & Chollet. 1995). 2. However, for Xenopus oocytes injected (into the nucleus) with 10 ng wild-type hNK2 receptor cDNA, a single 100 nM concentration of any of the three ligands resulted in complete desensitization to further concentrations. 3. On the other hand, none of the ligands caused any desensitization in oocytes injected with 0.25 ng wild-type hNK2 receptor cRNA. even at concentrations up to 10 microM. 4. The two N-terminally truncated analogues of neurokinin A have a lower efficacy than NKA and it is likely that it is this property which causes the observed differences in desensitization, rather than the formation of alternative active states of the receptor. 5. The peak calcium-dependent chloride current is not a reliable measure of maximal receptor stimulation and efficacy is better measured in this system by studying agonist-induced desensitization. 6. The specific adenylyl cyclase inhibitor SQ22536 can enhance NKA and GR64349-mediated desensitization which suggests that agonist-induced desensitization involves the inhibition of adenylyl cyclase and the subsequent down-regulation of the cyclic AMP-dependent protein kinase, possibly by cross-talk to a second signalling pathway.

The arrangement of the transmembrane helices in the secretin receptor family of G-protein-coupled receptors

The members of the secretin receptor family of G-protein-coupled receptors share no significant sequence similarity to the more familiar rhodopsin-like family. However, multiple sequence alignment analysis reveals seven hydrophobic regions with significant alpha-helical periodicity. Residues that are likely to be buried on the interior of the helical bundle and others that are likely to contact the lipid bilayer are identified. A predicted arrangement of the helical bundle is described in which, by comparison with the arrangement in the rhodopsin family, helices 2 and 7 are more buried within the bundle while helix 3 is more exposed to the lipid bilayer.

The conformational change responsible for AT1 receptor activation is dependent upon two juxtaposed asparagine residues on transmembrane helices III and VII

A model of the angiotensin AT1 receptor and site-directed mutagenesis were used to identify key residues involved in ligand binding. Receptors were stably expressed in human embryonic kidney 293 cells, and their binding properties compared. Wild type receptors exhibited low and high affinity binding sites for peptides. Substitution of Asn111, situated in the third transmembrane helix, resulted in a significant alteration in ligand binding with only high affinity binding of the peptides, angiotensin II, angiotensin III, and [p-amino-Phe6]angiotensin II and a marked loss in the binding affinity of the AT1 receptor selective non-peptide antagonist losartan. From our model it was apparent that Asn111 was in close spatial proximity to Asn295 in the seventh transmembrane helix. Substitution of Asn295, produced identical changes in the receptor's pharmacological profile. Furthermore, the Ser111AT1A and Ser295AT1A mutants did not require the association of a G-protein for high affinity agonist binding. Finally, the Ser295AT1A mutant maintained higher basal generation of inositol trisphosphate than the wild type, indicating constitutive activation. We propose that substitution of these residues causes the loss of an interaction between transmembrane helices III and VII, which allows the AT1 receptor to "relax" into its active conformation.

The ligand binding site of the neurokinin 2 receptor. Site-directed mutagenesis and identification of neurokinin A binding residues in the human neurokinin 2 receptor

Thirteen residues in the human neurokinin 2 (NK2) receptor were identified as potential ligand-binding residues by molecular modeling and amino acid sequence analysis. Site-directed mutagenesis was used to alter these residues in order to ascertain their importance in binding neurokinin A (NKA), the physiological peptide ligand for the NK2 receptor, and the non-peptide NK2 receptor selective antagonist SR48968. Four sites appear to be critical for NKA binding (Gln109, His198, Ile202, and Gly273). The mutant receptors Gln109-->His, Ile202-->Val, Gly273-->Pro, and Gly273-->Thr maintain their affinity for SR48968, despite being unable to bind the peptide ligand. His198-->Ala and His198-->Leu no longer bind NKA or SR48968. We have also identified a residue (Leu292) which appears to play a minor role in the binding of substance P (SP) and neurokinin B (NKB) to the NK2 receptor. The mutant receptor Leu292-->Ser binds NKB and SP with approximately a 5-fold greater affinity in comparison with the wild type receptor while the affinity of NKA remains unaffected. The results suggest that intramembranous residues, as well as residues which lie close to the extracellular side of transmembrane helices 3, 5, and 6, form part of the NK2 receptor binding site. Binding of SP and NKB to the NK2 receptor may also be influenced by residues near the extracellular side of helix 7. These results suggest that some regions of the binding site for NKA in the NK2 receptor are not used for binding SP in the NK1 receptor. However, it also seems that the NKA binding site includes regions that are also used by other G-protein-coupled receptors such as rhodopsin and the beta 2-adrenergic receptors.

The prediction and orientation of alpha-helices from sequence alignments: the combined use of environment-dependent substitution tables, Fourier transform methods and helix capping rules

Amino acid substitution tables are used to estimate the extent to which amino acids in families of homologous proteins are exposed to the solvent. The approach depends on the comparison of difference environment-dependent tables for solvent accessible/inaccessible residues with amino acid substitutions at each position in an aligned set of sequences. The periodicity in the predicted accessible/inaccessible residues is calculated using a Fourier transform procedure modified from that used to calculate hydrophobic moments. alpha-Helices are identified from the characteristic periodicities and the solvent accessible face of the helix is defined. The initial helix predictions are refined using rules for identifying the N- and C-termini of helices from sequence alignments. These rules have been defined from a study of protein structures. The combined method correctly predicts 79% of the residues in helices and incorrectly predicts only 12% of the nonhelical residues as helical. In addition, since the method is reliable at predicting the correct number of helices in the correct position in the sequence and since it also predicts the internal face of each helix, the results can be used to postulate 3-D arrangements of the secondary structure elements.