Comparison of the serum selenium content of healthy adults living in the Antwerp region (Belgium) with recent literature data.

Graphite furnace atomic absorption spectrometry, after improved matrix modification and using Zeeman background correction, was used to measure the serum selenium content of healthy adults living in the Antwerp region (Belgium). The mean serum concentration of 13 men and 13 women, sampled once a month during 1 year, was 84.3 +/- 9.4ng/ml with a broad range of 51.4-121.7 ng/ml. The intra-individual variation was remarkably high. Recent literature on selenium concentrations is reviewed and values are tabulated, with limitation to healthy adults and European countries. The mean serum selenium concentration measured corresponded well to older literature data for Belgium. The obtained values were found to be in the medium range compared with the literature data for other European countries.     

Rhythmic signalling and entrainment inVespa orientalis larvae: Characterization of the underlying interactions

Rhythmic “circa-second” contrations of larvae of the hornetVespa orientalis, believed to serve as hunger signals, were studied. A considerable degree of coordination among individual larvae, both in frequency and phase of these contractions, has been observed. The oscillations of singly isolated larvae are of short duration, non-constant, with increasing intervals in between and there is a substantial variability in the patterns shown by different larvae. In contrast, the association of two or more larvae leads to enhancement of their periodic behaviour and to (partial) entrainment. Communication among larvae may perhaps be mediated by the sound pulses (“scratching” noises) which are generated by these contractions. We have subjected individual and grouped larvae to external sound pulses and were able to demonstrate: (a) enhancement of rhythmic activity; (b) phase resetting; (c) entrainment to an external oscillator within a range of frequencies; (d) the existence of a subharmonic mode of entrainment. We propose a simple phenomenologic model to account for these larvae responses. Our model assumes the existence of an “energy” variable which declines with time but is upgraded, in a phase-dependent way, by external stimuli. Based in part on work performed by V. Barenholz-Paniry in partial fulfillment of the requirements for the M.Sc. degree from the Sackler Faculty of Medicine, Tel Aviv University, 1986.     

The mechanism of photodynamic inactivation ofStaphylococcus aureus by deuteroporphyrin

The mechanism ofStaphylococcus aureus inactivation by deuteroporphyrin (DT) and light was studied with singlet oxygen quenchers or hydroxyl radical scavengers. The light-activated DT (10 /ml) reduced the viability of the culture to less than 1%, whereas methionine, tryptophan, and 1,4-diazabicyclo-2,2,2-octane (DBCO) used as singlet oxygen quenchers provided almost 60% protection. Propylgallate, which is a hydroxyl free radical scavenger, also provided 60% protection. The presence of a singlet oxygen quencher and propylgallate provided almost complete protection from inactivation (96%). Photoinactivation in the absence of culture media (in saline) increased the killing rate and decreased the ability of the singlet oxygen quenchers to protect. In the same conditions damage from hydroxl free radicals was well protected by propyl gallate. The present results indicate thatS. aureus photoinactivation by DT and light is mediated by both singlet oxygen and hydroxyl free radicals.     

Desensitization of the Neurokinin 1 Receptor Is Mediated by the Receptor Carboxy-Terminal Region, but Is Not Caused by Receptor Internalization

Abstract: The carboxy-terminal cytoplasmic regions of the rat neurokinin 1 (substance P) and neurokinin 2 (neurokinin A) receptors have been exchanged to determine if this region of the neurokinin 1 receptor is involved in its desensitization. When expressed at similar levels in stably transfected Chinese hamster ovary (CHO) cell lines, receptors containing the carboxy-terminal region of the neurokinin 1 receptor desensitized significantly more (as measured by reduction of the inositol 1,4,5-trisphosphate response) when preexposed for 1 min to 1 µ M neurokinin, indicating a role for the carboxy-terminal region of the neurokinin 1 receptor in its desensitization. Measurement of receptor internalization using radiolabeled neurokinins (0.3 n M ) indicated that ∼75–80% of the receptors were internalized in each cell line after 10 min at 37°C, with no observable correlation between neurokinin receptor desensitization and internalization. Measurement of loss of receptor surface sites for cell lines CHO NK1 and CHO NK1NK2 following exposure to 1 µ M substance P also indicated no obvious relationship between the percent desensitization and percent of receptors internalized. Also, two inhibitors of neurokinin 1 receptor internalization, phenylarsine oxide and hyperosmolar sucrose, did not inhibit neurokinin 1 receptor desensitization. The protein kinase inhibitors Ro 31-8220, staurosporine, and Zn²⁺ had no effect on neurokinin 1 receptor desensitization, indicating that the kinases affected by these agents are not rate-limiting in neurokinin 1 receptor desensitization in this system.     

Sulfoxide configuration in sparsomycin determines time-dependent and competitive inhibition of peptidyl transferase

Sparsomycin, S_cR_s configuration, was the most potent of the four possible stereoisomers as a competitive inhibitor of peptide bond formation. In addition, the configuration of the two chiral centers dictated whether the compound exhibited time- and temperature-dependent inhibition of peptidyl transferase when incubated with polysomes prior to enzyme assay. The data corroborate the thesis that a peptidyl transferase-mediated acylation of the pivotal sulfoxide moiety and subsequent Pummerer rearrangement play a significant role in the inhibitory properties of sparsomycin.