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S L Meyer

Publications and source records attributed to S L Meyer.

At least 37 records · Page 2Linked to original sources
PubMed1989

Structure and regulation of the AMP nucleosidase gene (amn) from Escherichia coli.

The gene for AMP nucleosidase from Escherichia coli (amn) has been sequenced and characterized. The gene codes for a transcript of 1.7 +/- 0.2 kb, and the open reading frame corresponds to a protein of 483 amino acids (Mr = 53848). Amino acid sequences from tryptic peptides of AMP nucleosidase, N-terminal amino acid analysis, and the amino acid composition confirm the gene assignment and the open reading frame of amn. Primer extension studies determined the 5'-end of the amn transcript. The 5'-regulatory region contains overlapping sequences with similarity to the consensus sequences for binding cAMP receptor protein and inorganic phosphate repressor protein. Addition of exogenous cAMP to E. coli deficient in adenylate cyclase resulted in a 3-fold increase in AMP nucleosidase activity. Growth of E. coli on limiting phosphate resulted in an 8-fold increase in the production of AMP nucleosidase. The amn gene was expressed in AMP nucleosidase deficient strains of Azotobacter vinelandii and E. coli. A pUC-amn construct is described that causes approximately 20% of the total protein in E. coli to be produced as AMP nucleosidase. Comparison of the amino acid sequence for AMP nucleosidase with that for yeast AMP deaminase indicates a region in which six of eight amino acids are identical but no other overall homology. The amino acid sequence showed poor agreement with consensus sequences for adenylate binding sites even though the enzyme is known to have a catalytic site for AMP and regulatory sites for MgATP and phosphate.

Amino Acid Sequence↗
PubMed1989

Characterization of AMD, the AMP deaminase gene in yeast. Production of amd strain, cloning, nucleotide sequence, and properties of the protein.

The structural gene for AMP deaminase (AMD) from Saccharomyces cerevisiae has been cloned and characterized. A yeast strain deficient in AMP deaminase activity was produced and shown to be deficient in AMP deaminase protein by Western blot analysis. The gene for AMP deaminase was located in a lambda gt11 library of yeast genomic DNA, and a DNA fragment from the lambda gt11 clone was used to locate homologous DNA in a yeast genomic library in the centromeric plasmid YCp50, a yeast-Escherichia coli shuttle vector. One plasmid was selected for its ability to restore AMP catalytic activity to the deficient strain. Yeast deficient in AMP deaminase or those overproducing the enzyme grow at near normal rates. The open reading frame corresponding to AMD codes for a protein of 810 amino acids, molecular weight 93,286. The yeast AMD transcript is 3.0 +/- 0.2 kb, and the transcriptional initiation sites have been identified. Western blot analysis of extracts prepared from actively growing yeast indicates a major band at approximately 96,000 molecular weight with several bands at lower molecular weight, including 83,000. When the AMD gene is expressed in E. coli, the large Mr form of AMP deaminase is produced. These results show that the purified enzyme (Mr = 83,000) is a truncated form of the full-length translation product. No adenine nucleotide binding sites were located based on the consensus sequence from other nucleotide binding proteins. No overall homology was found between yeast AMP deaminase and E. coli AMP nucleosidase. Although their metabolic roles and regulatory mechanisms are similar, these enzymes have arisen from separate ancestral proteins.

AMP Deaminase↗
PubMed1988

Nuclear migration in a nud mutant of Aspergillus nidulans is inhibited in the presence of a quantitatively normal population of cytoplasmic microtubules.

Nuclear migration was studied in germinating conidia of a temperature-sensitive mutant of the fungus Aspergillus nidulans. At the restrictive temperature motility was demonstrably impaired because significantly fewer nuclei migrated into the germ tube relative to a population of similarly sized germlings grown at the permissive temperature. Further comparison of these populations showed that the mutant was leaky in that an increasing number of nuclei migrated as the total nuclear content increased in each germling. The restrictive temperature also induced elevated mitotic asynchrony and increased numbers of nuclei per germling. Serial section-based reconstruction of the microtubules in a freeze-substituted germling showed that they were not attached to the nucleus-associated organelles, were approximately parallel to the long axis of the germ tube, and seemed to be randomly distributed between the central and peripheral cytoplasm. Five germlings from each temperature were selected for quantitative analysis of cytoplasmic microtubules. All 10 germlings had typical nuclear migration phenotypes. No significant temperature-related difference in microtubule density was found. We conclude that inhibition of nuclear migration in the mutant is the effect of some defect other than the failure of cytoplasmic microtubules to assemble to their normal population density. We also suggest that nuclear motility is not dependent on mitosis-related microtubules.

Aspergillus nidulans↗
PubMed1986

Separate neural systems mediate the steroid-dependent and steroid-independent suppression of tonic luteinizing hormone secretion in the anestrous ewe.

In the ewe, two types of seasonal fluctuations in secretion of tonic luteinizing hormone (LH) have been described: a steroid-dependent change whereby estradiol gains the capacity to suppress LH pulse frequency in anestrus, and a steroid-independent decrease in pulse frequency in ovariectomized animals during anestrus. We have proposed that the former reflects activation, in anestrus, of estradiol-sensitive catecholaminergic neurons that inhibit gonadotropin-releasing hormone (GnRH). Three results reported here support this hypothesis: dopaminergic (pimozide) and alpha-adrenergic (phenoxybenzamine) antagonists increased LH in intact anestrous ewes without altering pituitary responses to GnRH; other dopaminergic (fluphenazine) and alpha-adrenergic (dibenamine) antagonists also increased LH in anestrus; agonists for dopaminergic (apomorphine) and alpha-adrenergic (clonidine) receptors suppressed LH secretion in both seasons, suggesting that the appropriate receptors are present in breeding-season ewes. In contrast, catecholamines do not appear to mediate the steroid-independent suppression of pulse frequency; neither pimozide nor phenoxybenzamine increased LH pulse frequency in ovariectomized ewes during anestrus. When antagonists for 6 other neurotransmitter receptors (muscarinic and nicotinic cholinergic, GABAnergic, serotonergic, opioid, and beta-adrenergic) were tested in anestrus, only cyproheptadine, the serotonergic antagonist, increased pulse frequency in ovariectomized ewes. Cyproheptadine had no effect on frequency during the breeding season. On the basis of these results, we propose that the steroid-dependent and -independent actions of anestrous photoperiod occur via catecholaminergic and serotonergic neurons, respectively.

Anestrus↗
PubMed1985

Neurotransmitters involved in mediating the steroid-dependent suppression of pulsatile luteinizing hormone secretion in anestrous ewes: effects of receptor antagonists.

Seasonal anestrus in the ewe results from two effects of inhibitory photoperiods: a steroid-dependent effect by which estradiol gains the capacity to suppress LH pulse frequency and a steroid-independent effect that decreases LH pulse frequency in ovariectomized ewes. We have previously proposed that these effects of anestrous photoperiods result from the activation of inhibitory neuronal mechanisms at this time of year. In the present study, we used specific receptor antagonists to test this hypothesis and identify the neurotransmitters involved. Initially, eight receptor antagonists were screened for their ability to increase pulsatile LH secretion in ovary-intact anestrous ewes. Of these, only pimozide, a dopaminergic antagonist, and phenoxybenzamine, an alpha-adrenergic antagonist, increased LH pulse frequency. In contrast, neither pimozide nor phenoxybenzamine increased pulsatile LH secretion in midluteal phase ewes during the breeding season. These drugs did, however, produce other biological responses at this time of year; pimozide increased serum PRL levels, and phenoxybenzamine decreased arterial blood pressure. Pimozide also increased pulsatile LH secretion in ovariectomized ewes treated with estradiol in anestrus to suppress LH pulse frequency, but phenoxybenzamine was ineffective in these animals. Neither drug increased LH in ovariectomized ewes not treated with estradiol. The seasonal variation in the ability of pimozide and phenoxybenzamine to increase LH secretion in ovary-intact ewes supports the hypothesis that inhibitory neural mechanisms suppressing GnRH are activated during anestrus and suggests that dopaminergic and/or alpha-adrenergic neurons are involved. In addition, the steroid-dependent effect of anestrous photoperiods may be exerted through the ability of estradiol to stimulate inhibitory dopaminergic neurons which are only active at this time of year.

Anestrus↗
PubMed1984

Effects of pentobarbital anesthesia on tonic luteinizing hormone secretion in the ewe: evidence for active inhibition of luteinizing hormone in anestrus.

In the ewe, seasonal anestrus appears to result from two effects of inhibitory photoperiod: 1) estradiol gains the capacity to suppress luteinizing hormone (LH) pulse frequency and hence becomes a potent inhibitor of tonic LH secretion and 2) a steroid-independent decrease in LH pulse frequency occurs in ovariectomized ewes. In this study, we have obtained evidence, using pentobarbital anesthesia, that both these actions of photoperiod reflect the activation, in anestrus, of an inhibitory neural system. Administration of pentobarbital to intact anestrous ewes produced a dramatic, 3-fold increase in LH pulse frequency during the 6 h of anesthesia. In contrast, during the breeding season, pentobarbital inhibited LH pulse frequency in luteal phase animals. There was also a seasonal variation in the effects of pentobarbital in ovariectomized ewes. During the breeding season this drug again suppressed LH secretion, inhibiting both LH pulse amplitude and frequency. In anestrus, pentobarbital also suppressed pulse amplitude, but it produced a transitory increase (lasting 3 h) in pulse frequency. To account for the stimulatory actions of pentobarbital, we propose that in anestrus, but not the breeding season, LH pulse frequency is held in check by a set of estradiol-sensitive inhibitory neurons. Further, we suggest that these neurons are activated by inhibitory photoperiod and account for both the steroid-dependent and steroid-independent actions of photoperiod.

Anesthesia↗
PubMed1981

Effect of adsorbed carbonate on surface charge characteristics and physical properties of aluminum hydroxide gel.

A titration procedure was used to determine the zero point of charge of a number of chloride-containing aluminum hydroxide gels and aluminum hydroxycarbonate gels. The surface charge characteristics of aluminum hydroxide gel were determined by both hydroxyls and the surface density of specifically adsorbed carbonate anion. The wide range of zero point of charge values reported for aluminum hydroxide is thought to be due to the presence of specifically adsorbed anions such as carbonate. The effect of ionic strength on the pH of aluminum hydroxide gel is important during washing since the ease of electrolyte removal is related to surface charge. Viscosity and sedimentation characteristics are related to the relationship between the zero point of charge and bulk pH. Maximum possibility was observed when the bulk pH was adjusted to the zero point of charge.

Adsorption↗
PubMed1979

Retrocorneal pigment proliferation after cataract extraction.

Retrocorneal pigment proliferation after cateract extraction is not rare. Downgrowths proliferate from fragments of iris pigment or peripheral iris in the corneal wound edges and occur slowly. Vision is affected if the central cornea is involved. Preventive measures include minimizing iris trauma and irrigating pigment fragments from the cornea and incision during surgery. In the study presented, patches of dislodged iris pigment epithelium were observed in 22 eyes. Lace-like downgrowths occurred in 18 eyes of 14 patients.

Adult↗
PubMed1978

Late wound separation after cataract extraction.

Many years after cataract extraction, blunt trauma ruptured limbal wounds in five eyes. Filtrations followed minor trauma in three patients, and occurred spontaneously in two others. Limbal wounds do not regain the tensile strength of adjacent normal stroma and may be further weakened by tissue incarcerations, vascularization, and other defects. Histologic studies after cataract extraction also reveal minimal collagen bridging of the stromal wound in some human eyes. Diagnosis and clinical significance are discussed.

Aged↗
PubMed1976

Influence of dobutamine on hemodynamics and coronary blood flow in patients with and without coronary artery disease.

The influence of dobutamine on hemodynamics and coronary blood flow was studied in patients after routine cardiac catheterization. The data demonstrated that dobutamine is a powerful inotropic agent at a dose that has a relatively small influence on heart rate. In patients without coronary artery disease dobutamine greatly increased coronary arterial perfusion. In patients with severe coronary artery diseases dobutamine resulted in a much smaller increase in coronary perfusion, and the pattern of perfusion became more inhomogeneous. The results suggest that dobutamine has a potential inotropic value but raise concern about its influence on regional myocardial perfusion in patients with serious coronary artery disease.

Blood Pressure↗
PubMed1976

Unstable angina pectoris. Clinical, angiographic, and myocardial scintigraphic observations.

The clinical, left ventricular and coronary angiographic data, and the technetium-99m stannous pyrophosphate (99mTc-PYP) myocardial scintigraphic results are presented in 31 patients with unstable angina pectoris. One-third of these patients had positive 99mTc-PYP myocardial scintigrams in a pattern suggesting limited and diffuse subendocardial necrosis. The positive 99mTc-PYP myocardial scintigrams occurred without diagnostic electrocardiographic and cardiac enzyme changes suggestive of myocardial infarction; positive scintigrams seemed to occur more commonly in patients with continuing pain after admission and in those without previous history of myocardial infarction. The positive 99mTc-PYP myocardial scintigrams did not correctly predict coronary anatomical patterns except that positive scintigrams occurred only in patients with coronary artery disease. Neither did the positive scintigrams necessarily occur in that group of patients with the poorest ventricular function though the 2 patients with the lowest ejection fractions both had positive 99mTc-PYP myocardial scintigrams. Finally, when positive 99mTc-PYP scintigrams are the only evidence suggestive of limited subendocardial infarction in patients with unstable angina pectoris, they do not appear to have any prognostic significance in terms of longevity or response to pharmacological or surgical therapy, though the follow-up period so far is short.

Adult↗
PubMed1975

Acute subendocardial myocardial infarction in patients. Its detection by Technetium 99-m stannous pyrophosphate myocardial scintigrams.

Eighty-eight patients admitted to a coronary care unit with chest pain of varying etiology but without ECG evidence of an acute transmural myocardial infarction had myocardial scintigrams using technetium-99m stannour pyrophosphate (99m-Tc-PYP). Seventeen of these patients had ECG and enzymatic evidence suggestive of acute subendocardial myocardial infarction. In each of these the scintigrams were postivie demonstrating increased 99m-Tc-PYP uptake either in a faintly but diffusely positive pattern or in a well-localized strongly positive one. The remaining 71 patients did not evolve ECG or enzymatic evidence of acute myocardial infarction. In each of these patients the myocardial scintigram was negative. Thus 99m-Tc-PYP myocardial scintigrams are capable of identifying the presence of acute subendocardial myocardial infarction in patients. The absolute frequency with shich subendocardial myocardial infarction can be recognized utilizing this technique will have to be established in a larger number of patients in the future.

Acute Disease↗
PubMed1975

Technetium stannous pyrophosphate myocardial scintigrams in patients with chest pain of varying etiology.

Technetium-99m stannous pyrophosphate was utilized for myocardial imaging in 202 patients admitted to the hospital with chest pain of uncertain etiology. One hundred and one patients had clinical and evolved electrocardiographic and enzymatic evidence of acute myocardial infarction. Ninety-six of these 101 patients had increased myocardial uptake of the technetium stannous pyrophosphate and positive myocardial scintigrams; there was nearly precise correlation between the ECG and myocardial imaging localization of the area of infarction for acute transmural myocardial infarctions. In the five patients with negative myocardial images the scintigrams were obtained after seven or more days had elapsed following the myocardial infarction. In the remaining 101 patients no clinical, ECG, or enzymatic evidence of infarction developed; 92 of these patients had negative myocardial scintigrams. Seven of the remaining nine patients were admitted with "unstable angina pectoris", and despite the absence of diagnostic ECG and enzyme evolution each of these patients had faintly and diffusely positive myocardial scintigrams. The remaining two patients had positive myocardial scintigrams but no definite ECG or enzymatic evidence of acute myocardial infarction. Thus the technetium pyrophosphate imaging technique appears safe, inexpensive and to correlate well with ECG and enzyme identification of the presence of infarction and with ECG localization of myocardial infarction. In addition the positive myocardial scintigrams in some patients with "unstable angina" suggest that there may be limited myocardial necrosis that is ordinarily undetected by ECG and enzymes in these patients. The incidence of false positive and false negative scintigrams appears to be small.

Angina Pectoris↗