Melatonin action on thyroid activity in the soft-shelled turtle, Lissemys punctata punctata

Adult female turtles (Lissemys punctata punctata) were treated with pineal indoleamine melatonin (100 micrograms/100 g) or the antithyroid agent, methylthiouracil (100 micrograms/100 g) or melatonin together with methylthiouracil (100 micrograms of each drug/100 g) for 12 days. Melatonin alone inhibited thyroid activity as evidenced by reduction in the gland weight, follicular epithelial cell height, thyroid peroxidase, and plasma thyroxine levels. Methylthiouracil caused hyperplasia of the gland, although it inhibited thyroid activity and reduced thyroid peroxidase and plasma thyroxine levels. Melatonin together with methylthiouracil produced changes similar to those obtained with melatonin alone. The results indicate that melatonin probably exerts inhibitory effects influences on both thyrotropin release from the pituitary and the activity of the thyroid itself in turtles.     

Structure of cell-wall teichoic acids in Streptomyces roseoflavus var. roseofungini and its Nocardia-like variant

The structure of teichoic acids was studied in the cell walls of Streptomyces roseoflavus var. roseofungini 1128 and its Nocardia-like variant 1-68 differing from the parent strain in the absence of a spore-forming aerial mycelium as well as by the fragmentation of hyphae in the substrate mycelium. The teichoic acids of the both cultures consist of a 1,3-poly(glycerophosphate) chain containing 11-13 glycerolphosphate residues which have glucosamynl units and lysine groups bound through an ester bond. These teichoic acids contain no O-acetyl groups, in contrast to the glyceroteichoic acids of actinomycetes studied earlier. The teichoic acid from the cell wall of the variant has less lysine and glucosamine then the parent strain. The content of teichoic acid in the cell wall of the parent culture is 4.5 times greater than in the wall of the variant.     

Multiple frequency tympanometry: effects of ear canal volume compensation on static acoustic admittance and estimates of middle ear resonance

Three methods for compensating multiple frequency acoustic admittance measurements for ear canal volume were studied in 26 men with normal middle ear transmission systems. Peak compensated static acoustic admittance (magnitude of y) and phase angle (phi) were calculated from sweep frequency tympanograms (226-1243 Hz in 113 Hz increments). Of the procedures used to compensate for volume in rectangular form, the ear canal pressure used to estimate volume had the largest effect on the estimate of middle ear resonance. Median resonance was 800 Hz for admittance measurements compensated at 200 daPa versus 1100 Hz for measurements compensated at -350 daPa. The remaining two methods, compensation of susceptance only versus both susceptance and conductance and compensation using the minimum volume versus separate volumes at each frequency, did not affect estimates of middle ear resonance. Estimates of middle ear resonance from compensated phase angle measurements also were compared with estimates of resonance from admittance and phase difference curves. Although resonance could not be estimated from the phase difference curve, resonance estimated from the admittance difference curve agreed with the estimate from compensated phase angle.     

The crystal structure of domain 1 of receptor protein-tyrosine phosphatase mu

Receptor-like protein-tyrosine phosphatases (RPTPs) play important roles in regulating intracellular processes. We have been investigating the regulation and function of RPTPmu, a receptor-like PTP related to the Ig superfamily of cell adhesion molecules. Recently, the crystal structure of a dimer of the membrane proximal domain of RPTPalpha (RPTPalpha D1) was described (Bilwes, A. M., den Hertog, J., Hunter, T., and Noel J. P. (1996) Nature 382, 555-559). Within this crystal structure, the catalytic site of each subunit of the dimer is sterically blocked by the insertion of the N-terminal helix-turn-helix segment of the dyad-related monomer. It was proposed that dimerization would lead to inhibition of catalytic activity and may provide a paradigm for the regulation of the RPTP family. We have determined the crystal structure, to 2.3 A resolution, of RPTPmu D1, which shares 46% sequence identity with that of RPTPalpha D1. Although the tertiary structures of RPTPalpha D1 and RPTPmu D1 are very similar, with a root mean square deviation between equivalent Calpha atoms of 1.1 A, the quaternary structures of these two proteins are different. Neither the catalytic site nor the N-terminal helix-turn-helix segment of RPTPmu D1 participates in protein-protein interactions. The catalytic site of RPTPmu D1 is unhindered and adopts an open conformation similar to that of the cytosolic PTP, PTP1B (Barford, D., Flint, A. J., and Tonks, N. K. (1994) Science 263, 1397-1404). We propose that dimerization-induced modulation of RPTP activity may not be a general feature of this family of enzymes.     

Addressing coronary heart disease risk in women

Contrary to popular perceptions, coronary heart disease (CHD) is a serious and widespread problem in US women. Public education, preventive interventions, and better data on CHD risk and prevention in women are needed.     

Construction of a DNA probe to detect isoquinoline-degrading bacteria

To facilitate the cloning of DNA encoding isoquinoline degradation an assay was developed that allowed the rapid visual scoring of the isoquinoline degradation phenotype of single colonies. Transposon mutagenesis of one of the isolates. Comamonas acidovorans IQ3, was performed using Tn5, and nine Isq-mutants deficient in the ability to utilise isoquinoline as the sole nitrogen source were isolated. These mutants were also incapable of utilising the first metabolite of the isoquinoline degradation pathway, 1-hydroxyisoquinoline, as the sole carbon source. For each Isq-mutant, the EcoRI fragment containing the Tn5 insertion was cloned into pBR322. Restriction and Southern analyses of the cloned DNA revealed that of the nine Isq-mutants, six contained Tn5 insertions in a common 8.9-kb EcoRI fragment derived from the wild type, C. acidovorans IQ3. The cloned DNA thought to be involved in the degradation of isoquinoline proved to be specific when used as a probe in colony hybridization to some bacteria possessing the ability to degrade isoquinoline.     

Achalasia of the esophagus

Achalasia, a disease of unknown cause, is characterized by absence of peristalsis in the esophagus body and incomplete relaxation of the lower esophageal sphincter (LES) in response to swallowing. This article reviews the history and pathogenesis of achalasia along with clinical manifestations, diagnosis and management options relating to the disease.