The degradation of acetylcholine receptor observed in denervated and innervated normal rat diaphragms in organ culture is stimulated by exogenous antireceptor serum. In this paper we demonstrate that diaphragms from rats with experimental autoimmune myasthenia gravis contain reduced amounts of acetylcholine receptor. Acetylcholine receptor from myasthenic, but not from normal, rats has antibody bound to it and is degraded at an accelerated rate. We conclude that in the chronic phase of experimental autoimmune myasthenia gravis increased acetylcholine receptor degradation can be accounted for by a mechanism involving antigenic modulation, and that such a process can contribute to the clinical symptoms of impaired neuromuscular transmission. 相似文献
Summary In the present study an attempt was made to demonstrate melatonin in the rat pineal gland by means of immunohistochemistry. The anti-body used was raised against 5-methoxy-N-acetyltryptophan which is chemically similar to melatonin. Specific fluorescence was demonstrable only in pineals from rats killed during the night, when melatonin formation is high. It was restricted to parenchymal cells lying in a marginal zone of the organ. These results are discussed in relation to a subdivision of the pineal parenchyma into cortical and medullary areas.Supported by a grant of the Deutsche Forschungsgemeinschaft (VO 135/4) within the Schwerpunktprogramm Neuroendokrinologie 相似文献
Raman spectra of antenna chlorophyll a and chlorophyll b were selectively obtained from chloroplasts of green plants and from monocellular algae, using resonance enhancement in the respective Soret bands of these molecules, at 35 K. It is shown that:
Antenna chlorophyll a molecules occur in at least five discrete categories, distinguished by different extramolecular bonding of their 9-keto carbonyl groups.
These vibrational categories are probably identical in nature and number among the different organisms studied, but differ in their relative populations.
Chlorophyll b molecules occur in at least two different categories differing by the strength of the interactions of their 3-formyl C = 0 groups. These vibrational categories also appear as universal.
Most chlorophyll a and b molecules have their magnesium atoms bound to a single foreign ligand, whose nature may depend on the population considered.
Resonance Raman spectra of antenna structures, including those of organisms devoid of chlorophyll b, were compared to resonance Raman spectra of chlorophyll a and b in monomeric, oligomeric and hydrated polymeric states, at room temperature and at 35 K. No sizable amount of antenna chlorophyll a or b occurs as dry or hydrated oligomers, or polymers. The antenna molecules are thus necessarily bound to foreign molecules, probably proteins, through H-bonding on their formyl and/or keto carbonyl groups and through bonding of their magnesium atoms. 相似文献
In an accompanying publication by Duckwitz-Peterlein, Eilenberger and Overath ((1977) Biochim. Biophys. Acta 469, 311–325) it is shown that the exchange of lipid molecules between negatively charged vesicles consisting of total phospholipid extracts from Escherichia coli occurs by the transfer of single lipid monomers or small micelles through the water. Here a kinetic interpretation is presented in terms of a rate constant, , for the escape of lipid molecules from the vesicle bilayer into the water. The evaluated rate constants are and for phospholipid molecules with and , respectively, as the predominant acyl chain component. The rate constants are discussed in terms of the acyl chain and polar head group composition of the lipids. 相似文献
The cyclic aliphatic sulfuric acid esters 1,2-ethylene sulfate (ESF), 1,3-propylene sulfate (PSF) and 1,3-butylene sulfate (BSF) have been tested for their mutagenic and DNA-damaging activity. Mutagenicity of the compounds was established with his-auxotrophic indicator strains of Salmonella typhimurium using the in vitro plate test and the host-mediated assay technique with mice as host animals. The DNA-damaging activity was tested in a repair test with Proteus mirabilis mutants defective in DNA repair.In the repair test with a set of P. mirabilis strains (PG713 hcr?rec?: PG273 hcr+rec+) PSF and BSF showed a preferential growth inhibition of the repair-defective strain suggesting DNA-damaging activity of these chemicals. No such activity was found for ESF using the same concentrations of 5 and 15 μmol/plate.All cyclic sulfates revert the tester strain TA1535 of S. typhimurium in vitro indicating their ability to induce base substitutions. Compared with the reference compounds dimethyl sulfate (DMS), diethyl sulfate (DES), 1,3-propane sulfone (PPS) and 1,4-butane sulfone (BTS) the mutagenic activity in the plate test can be described as follows: PPS > PSF > BSF > BTS > ESF > DES > DMS.Dose-response studies in the host-mediated assay with tester strain TA1950 of S. typhimurium as genetic indicator system revealed a linear dosedependency of mutagenic activity. For PPS and PSF the lowest effective dose (LED) has been established as 10 μmol/kg. The LED for BSF and BTS was 50 μmol/kg, DMS and DES were mutagenic in doses of 2500 μmol/kg, while ESF was only weakly mutagenic with a LED of 5000 μmol/kg.The dose-response studies in the host-mediated assay and the results obtained in the in vitro spot test demonstrate similarities in the mutagenic action of the cyclic sulfates PSF and BSF and the respective sulfones, while the stronger alkylating compound ESF was a weak mutagen both in vitro and in vivo. 相似文献
Various parameters of the rat pineal gland display a 24-h rhythm. However, nothing is known about possible 24-h variations in cyclic GMP (cGMP) metabolism. In the present study, 24-h variations in pineal gland cGMP accumulation were investigated by determining the increase in cGMP level with and without inhibitors of phosphodiesterase at different time points over a light/dark cycle (12/12 h). Furthermore, the activity of guanylate cyclase (GC) was determined under substrate-saturated conditions regarding the cytosolic and particulate forms of the enzyme. It has been found that cGMP accumulation and GC activity display biphasic 24-h variations with two peaks--one approximately 7 h after lights "on" and the other approximately 7 h after lights "off." The activity of cytosolic GC remains unchanged in the presence of the nitric oxide (NO) synthesis inhibitor N-monomethyl-L-arginine, indicating that 24-h variations in the activity do not reflect changes in the synthesis of the GC stimulator NO. 相似文献
On the basis of molecular dynamics and free-energy perturbation approaches, the Glu46Gln (E46Q) mutation in the guanine-specific ribonuclease T1 (RNase T1) was predicted to render the enzyme specific for adenine. The E46Q mutant was genetically engineered and characterized biochemically and crystallographically by investigating the structures of its two complexes with 2'AMP and 2'GMP. The ribonuclease E46Q mutant is nearly inactive towards dinucleoside phosphate substrates but shows 17% residual activity towards RNA. It binds 2'AMP and 2'GMP equally well with dissociation constants of 49 microM and 37 microM, in contrast to the wild-type enzyme, which strongly discriminates between these two nucleotides, yielding dissociation constants of 36 microM and 0.6 microM. These data suggest that the E46Q mutant binds the nucleotides not to the specific recognition site but to the subsite at His92. This was confirmed by the crystal structures, which also showed that the Gln46 amide is hydrogen bonded to the Phe100 N and O atoms, and tightly anchored in this position. This interaction may either have locked the guanine recognition site so that 2'AMP and 2'GMP are unable to insert, or the contribution to guanine recognition of Glu46 is so important that the E46Q mutant is unable to function in recognition of either guanine and adenine. 相似文献
Summary The products of 11 switching (swi) genes are required for efficient mating-type (MT) switching in homothallic (h90) strains of Schizosaccharomyces pombe. The MT region of h90 comprises three cassette genes: the expression site mat1: 1 and two silent loci, mat2: 2 and mat3: 3. Besides reducing MT switching, the swi6 mutation leads to deletions in the MT region caused by intrachromosomal cross-overs between two paired cassettes. These deletions only arise if DNA double-strand breaks are present at mat1: 1, which initiate MT switching. Furthermore, swi6 allows meiotic recombination in the K region, a region of 16 kb between mat2: 2 and mat3: 3; in wild-type strains no recombination occurs in K. swi6 also allows the simultaneous expression of two different cassettes in the same haploid cell. Thus swi6 may have an influence on the general chromatin structure in the MT region. 相似文献
Intact turtle brain provides a useful model for the study of anoxia and potential survival strategies, since this tissue maintains transmembrane ion gradients and ATP levels during prolonged anoxia and recovers functional activity afterwards. Since isolated tissues offer experimental advantages, the present study sought to determine effects of anoxia on the isolated turtle cerebellum and to define relationships between anoxia survival and glucose supply. In normoxia, the extracellular potassium ([K+]o) activity and evoked potentials were maintained with 5 mM glucose, but 20 mM glucose was required to maintain adenosine triphosphate (ATP) levels and prevent significant increases in [K+]o during anoxia. Inhibition of glycolysis by iodoacetic acid (IAA) during anoxia provoked large increases in [K+]o at all glucose levels. These results demonstrate the usefulness of the isolated turtle cerebellum for studies of anoxic survival since this tissue can maintain ATP levels and [K+]o during prolonged anoxia with 20 mM glucose in the artificial cerebrospinal fluid medium. They also suggest the presence of a Pasteur effect at least during the transition to a hypometabolic state. 相似文献