A proton nuclear magnetic resonance study of gamma-glutamyl-amino acid cyclotransferase in human erythrocytes

Spin-echo NMR spectroscopy was shown to be a reliable technique for the monitoring of the in situ cleavage of gamma-Glu-Ala by gamma-glutamyl-amino acid cyclotransferase in whole erythrocytes and hemolysates. Of particular importance was the difference in chemical shifts between peptide resonances and those of the constituent amino acids. Using lysates of varying dilution, it was shown that the specific activity of the enzyme was not concentration-dependent, thus suggesting a lack of cytosolic low-molecular-weight-effectors or enzyme dissociation. Furthermore, the initial velocities of the reaction as a function of substrate concentration obeyed Michaelis-Menten kinetics with a Km = 2.0 +/- 0.3 mmol/l and Vmax = 137 +/- 7 mmol/h/l of cell water in 1H2O medium. Similar analysis in 2H2O medium revealed a solvent kinetic isotope effect of 1.9 +/- 0.4 at low substrate concentrations. The implications of this observation for the mechanism of the reaction are discussed. Cleavage of the peptide by a suspension of intact erythrocytes was at a rate 300 times less than the corresponding lysate flux, thus indicating the rate limitation by transport in the coupled system.     

Effect of brain acid extract products in inbred mice on 3H-diazepam reception

The influence of brain acid extract products, isolated by high-performance liquid chromatography on H3-diazepam binding was investigated in synaptosomal membranes of C57BL/6 and BALB/c mice. Fractions with stimulatory and inhibitory activity were isolated. Quantitative and qualitative differences in the effects and structure of ACTH-immunoreactive peptide fractions under study were established.     

Cell Cycle activation and ouabain-sensitive ion movements of 3T3 and C3H-10T½ fibroblasts

The introduction of either PGF_2α (10^?7 M) or TPA (10^?7 M) stimulated, ouabain-sensitive ⁸⁶Rb⁺ influx at 30 min in postconfluent 3T3-4 mouse fibroblast cultures by 117% and 124%, respectively. Both TPA and PGF_2α at these concentrations stimulated the incorporation of ³H-TdR into DNA. TPA had the greatest stimulatory effect, which was similar to that obtained with 10% fetal calf serum. In accord with the idea that modulation of membrane processes such as Na⁺/K⁺ pump activity in fibroblasts may reflect important events related to the initiation of DNA synthesis, it was observed that in both 3T3-4 and C3H-1 0T½ cells there were parallel increases in ³H-TdR incorporation and ouabain-sensitive ⁸⁶Rb⁺ influxes with 10^?7 M TPA, whereas PGF_2α stimulated a significant increase in ³H-TdR incorporation in 3T3-4 but not C3H-10T½ cells and only marginal increases in ouabain-sensitive ⁸⁶Rb⁺ influx in both. Therefore, although there appears to be a close correlation between Na⁺/K⁺ pump activation and subsequent S-phase entry following TPA stimulation, a similar correlation for PGF_2α cannot be confirmed.     

III. Serum and sputum immunoglobulin E levels in respiratory diseases in adults

Using a solid-phase radioimmunoassay, serum IgE level was determined in 46 normal subjects, 53 patients with bronchial asthma, 44 patients with chronic bronchitis and / or emphysema, and 19 patients with restrictive lung disease. Sputum IgE was measured simultaneously in 51 of the subjects. The range of serum IgE concentration in the normal subjects was wide. It varied between 15 and 750 ng/ml with a mean of 135 ng. Asthmatic patients had significantly higher levels of serum IgE with a mean of 579 ng/ml, but only 30% fell outside the normal 95% confidence limits. Patients with chronic bronchitis, emphysema and restrictive lung diseases had normal IgE levels. There was a significant correlation between serum and sputum IgE levels.     

Preface to Mechanisms of neuromuscular control. A Theme organized and edited by J. L. van Leeuwen

Preface to Mechanisms of neuromuscular control. A Theme organized and edited by J. L. van Leeuwen.     

Putative candidate genes for blood pressure control in the SHR.BN-RNO8 congenic substrains

The SHR-Lx congenic strain carrying a differential segment of chromosome 8 of BN and PD origin was recently shown to exhibit a significant decrease in blood pressure as compared to the SHR strain. There were two positional candidate genes for blood pressure control mapped to the differential segment: the rat kidney epithelial potassium channel gene (Kcnj1) and brain dopamine receptor 2 gene (Drd2). Bot these genes were separated into SHR.BN-RNO8 congenic substrains. In this communication, we are presenting the assignment of two further putative candidate genes, which might be involved in blood pressure control to the BN/PD differential segment of the SHR-Lx congenic strain. These are: the gene coding for smooth muscle cell specific protein 22 (Sm22) defined by the D8Mcw1 marker and neuronal nicotinic acetylcholine receptor gene cluster, defined by the D8Bord1 marker. Moreover, the glutamate receptor gene Grik4 which also maps to the differential segment of the SHR-Lx should be taken into account. The genetic separation of all these putative candidate genes of blood pressure control is being performed by recombinations and subsequent selection using (SHR×SHR-Lx) intercross population.     

Repetitive excitation of bursts of action potentials in the rat hippocampus following single shock stimulation

1. Post-stimulus time (PST) histograms of rat hippocampal cells were recorded in vivo following single-shock stimulation of the fornix. 2. The PST histograms displayed a series of peaks of decreasing amplitude, similar to damped oscillatory responses previously recorded in cats and rabbits. 3. The effect of increased background activity was investigated by recording histograms with concurrent pulse train stimulation of the contralateral hippocampus. The histograms showed a decreased latency to the onset of the second peak. 4. Damped oscillatory activity seen in the in vivo rat preparation could not be elicited in the in vitro rat slice preparation. Thus species differences cannot account for the absence in slice studies of this type of damped oscillatory activity. 5. We conclude that the level of spontaneous activity is one factor contributing to the genesis of multiple peaks in histograms in the in vivo preparation.