Interaction between dialkylamines and bacterial agmatinase]

It was demonstrated that aliphatic dialkylamines are more effective inhibitors of bacterial agmatinase than monoalkylamines and differ from the latter by the type of inhibition. The dependence of the inhibition constant on the hydrophobicity of the compounds tested was studied. The type of this dependence was found to be different for long- and short-radical dialkylamines, the correlation equation appearing as 1g(1/Ki) = 0,33 1gPo + (2,3 +/- 0,2) for the former compounds and as 1g(1/Ki) = 1,0 1gPo + (2,2 +/- 0,2) for the latter. The enzyme inhibition by the inhibitors tested was dependent on pH: e. g. with an increase in pH the inhibiting effect was decreased. It was assumed that the inhibitor sorption by agmatinase is of hydrophobic-ionic type and that the active site of the enzyme contains two hydrophobic zones separated by a nucleophylic group. The length of the hydrophoblic zones was estimated.     

Carbamyl phosphate and citrulline formation by phototrophic bacteria

The purple bacteria Ectothiorhodospira shaposhnikovii and Rhodospirillum rubrum are capable of synthesizing citrulline in the presence of ammonium hydrocarbonate, ornithine, ATP and Mg2+ ions. Citrulline biosynthesis by these phototrophic bacteria is presumed to be catalysed by carbamate kinase and ornithine transcarbamoylase. Therefore, certain phototrophic bacteria can assimilate carbon dioxide and ammonia for biosynthesis of amino acids, in particular, citrulline and, apparently, arginine.     

A new endemic species of Helichrysum Gaertn. (Asteraceae-Inuleae) from south Anatolia

A new species of Helichrysum Gaertn., H. orbicularifolium Sümbül, R. S. Göktürk & O. D. Düşen sp. nov. , is described and illustrated. The species is restricted to the south Anatolia Province, Antalya, Turkey, growing in humid calcareous rock crevices and on limestone cliffs. The species is compared with the closely related H. chasmolycicum . © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 141 , 251–254.     

A circadian rhythm of locomotor activity in newly emerged Ceratophyllus sciurorum

Abstract Circadian rhythm in newly emerged individuals of the Red Squirrel ( Scuirus vulgaris ) flea C.s. sciurorum was studied in a constant environment, using an insect activity monitor. Trials were run over 7 days using two start times (08.00 and 17.00 hours). The results show that, regardless of start time, the fleas display a 24 h activity rhythm. The presence of a rhythm under constant conditions gives a strong indication that C. s.sciurorum has a self-sustaining clock which is started by disturbance and is most likely to be linked to host activity patterns.     

The biosynthesis of carbamoyl phosphate by Ectothiorhodospira shaposhnikovii and its utilization in carbamoylation reactions

Abstract Carbamoyl phosphate is synthesized by the purple bacterium Ectothiorhodospira shaposhnikovii from CO₂, NH₃ and ATP and is used for enzymatic transfer of the carbamoyl moiety to ornithine. In addition to this reaction nonenzymatic carbamoylation of some amino derivatives occurs, especially at high concentrations of the carbamoyl acceptors and at a temperature of about 45°C. The role of such reactions is discussed.     

Linear theory of the interaction of an electron beam with electromagnetic waves in the ion focus regime in a pasotron

A study is made of the interaction of an electron beam focused by a positive ion background with electromagnetic waves in a pasotron—a modern plasma microwave electronics device with long-term interaction in the ion focus regime.     

Millimeter-wave effects on electric activity of crayfish stretch receptors

The effects of super high frequency (SHF) microwaves (34-78 GHz) on rates of spontaneous firing of the slowly adapting, stretch-receptor neurons of crayfish were studied. Initially, irradiation of continuously perfused, fluid-cooled preparations at power densities to 250 mW/cm2 caused a transient decrease in the rate of spontaneous firing (the dynamic response). Subsequently, with extinction of the SHF field, the rate of firing increased, finally stabilizing at pre-exposure levels (stationary phase). Rates of firing also increased when the receptor muscle was stretched, and they were inversely correlated with small, field-induced increases of temperature (approximately 1.5 degrees C). The response to SHF radiation did not depend on frequency if temperature of the medium was constant. No resonant peaks were found when the millimeter range of frequencies was scanned.