External factors involved in the regulation of an extracellular proteinase synthesis in Bacillus megaterium

Summary A mathematical model was formulated to describe the kinetics and stoichiometry of growth and proteinase production in Bacillus megaterium. Synthesis of the extracellular proteinase in a batch culture is repressed by amino acids. The specific rate of formation of the enzyme (r _E) can be described by the formula {ie373-1}, where k ₂ and k ₃ stand for the non-repressible and repressible part of enzyme synthesis respectively, k _{S 2} is a repression coefficient and S ₂ indicates the concentration of amono acids; the values of k ₂ and k _{S 2} depend on the composition of the mixture of amino acids. Even in a high concentration, a single amino acid is less effective than a mixture of amino acids. The dependence of the proteinase repression on the concentration of an external amino acid (leucine) follows the same course as its rate of incorporation into proteins, approaching saturation at concentrations higher than 50 M (half saturation approximately 10 M). However, the total uptake of leucine did not exhibit any saturation even at 500 M external concentration.Symbols X biomass concentration, g/l - E proteinase concentration, unit/l - t time, h - S ₁ concentration of glucose, g/l - S ₂ concentration of amino acids, g/l - specific growth rate, l/h - rE specific rate of enzyme production, unit/g/h - k ₁ growth kinetic constant, l/h - k ₂ product formation kinetic constant (for non-repressible part of enzyme synthesis), unit/g - k ₃ product formation kinetic constant (for repressible portion of enzyme synthesis), unit/g - k _{S 1} saturation constant, g/l - k _{S 2} repression coefficient for a certain amino acid or amino acids mixture, g/l     

Characterization of the Actions of Toxins II-9.2.2 and II-10 from the Venom of the Scorpion Centruroides noxius on Transmitter Release from Mouse Brain Synaptosomes

Toxic peptides II-9.2.2 and II-10, purified from Centruroides noxius venom, bear highly homologous N-terminal amino acid sequences, and both toxins are lethal to mice. However, only toxin II-10 is active on the voltage-clamped squid axon, selectively decreasing the voltage-dependent Na+ current. Here, we have tested toxins II-9 and II-10 on synaptosomes from mouse brain: both toxins increased the release of gamma-[3H]aminobutyric acid ([3H]GABA). Their effect was completely blocked by tetrodotoxin or by the absence of external Na+. Also, both toxins increased Na+ permeability in isolated nerve terminals. Besides the observation that toxin II-9 is active on synaptosomes, the effect of toxin II-10 in this preparation is opposite to that observed in the squid axon. Thus, our results reflect functional differences between the populations of Na+ channels in mouse brain synaptosomes and in the squid axon. The release of GABA evoked by these toxins from synaptosomes required external Ca2+ and was blocked by Ca2+ channel blockers (verapamil and Co2+). This latter observation is in sharp contrast to the releasing action of veratrine, which evoked release even in the absence of external Ca2+. Furthermore, the action of both C. noxius toxins was potentiated by veratrine, a result suggesting they have different mechanisms of action. Among drugs that release neurotransmitters by increasing Na+ permeability, it is noteworthy that scorpion toxins are the only ones yet reported to have a strict requirement for external Ca2+.     

Progress since the first international symposium: ‘Genetic aspects of plant mineral nutrition’, Beograd, 1982, and perspectives of future research

Summary The paper discusses the problems of genetic aspects of plant mineral nutrition in the light of the results presented at the First and Second Symposia on ‘Genetic Aspects of Plant Mineral Nutrition’ organized in Beograd in 1982 and Madison in 1985, respectively. On the basis of the results, future directions of research are discussed. The papers deal with the concentration and content of mineral nutrients in different genotypes, physiological and biochemical aspects of the genetic specificity of plant mineral nutrition, relations between plant genotypes and nitrogen fixing micro-organism strains, as well as with some related problems which have been investigated to a lesser extent. Particular attention is paid to papers and problems referring to genetic and breeding research work linked with genetic aspects of plant mineral nutrition as well as the possibilities of developing new cultivars requiring certain soil and mineral nutrition conditions for their cultivation.     

Xfin: an embryonic gene encoding a multifingered protein in Xenopus.

The Xenopus laevis genome was screened for putative DNA-binding gene products by using the 'finger' region of the Drosophila gene Krüppel as a probe. The one gene detected, named Xfin, codes for a protein with 37 finger domains that comprise nearly 90% of the protein. In the light of studies by Rhodes and Klug (Cell, 46, 123-132, 1986), these data suggest that the Xfin protein has the capacity to bind an unusually large stretch (185 bases) of DNA. The Xfin gene is expressed as a maternal and zygotic mRNA that undergoes extensive polyadenylation changes during early development. The Xfin mRNA expression pattern and the potential DNA binding activity of the protein point to the possibility that the Xfin gene may have a role in controlling gene activity during early embryonic development.     

Changes in H1 complement in differentiating rat-brain cortical neurons

Neuronal nuclei have a low H1 content. A stoichiometry of 0.47 molecule/nucleosome, on average, is calculated for rat brain cortical neurons by comparing its H1 content with that of liver nuclei. The H1 fraction of rat cerebral cortex neurons has been resolved into five subtypes, H1a--e, that have the same mobility as the unphosphorylated H1 forms of other rat tissues. The subtypes H1a--d decay exponentially during postnatal development and are substituted to different extents by H1e. The higher replacement rate is shown by H1a with an apparent half-lifetime of about 5 days. The corresponding values for H1b, H1c and H1d are 11, 21 and 15 days. Several conclusions can be drawn from the observation of postnatal changes in H1 subtype proportions. The low H1 content of neuronal nuclei does not imply the presence of notable peculiarities in subtype composition or in subtype substitution pattern. There is turnover of H1 in differentiating neurons once cell proliferation and DNA replication have ceased. The relative rates of synthesis and/or degradation of the subtypes differ in germinal cells and in neurons. Comparison with previous results on H1 degrees accumulation also shows that in cortical neurons the regulation of the subtypes H1a--e differs from that of H1 degrees.     

Chromaffin cell calcium channel kinetics measured isotopically through fast calcium, strontium, and barium fluxes

Fast Ca2+ uptake into K+-depolarized cultured bovine adrenal chromaffin cells has been isotopically measured in a time scale of 1-10 s. Depolarized cells retained as much as 80-fold 45Ca2+ taken up by resting cells; Ca2+ was not taken up by fibroblasts or endothelial-like cells. Because Ca2+ entry was inhibited by inorganic (La3+, Co2+, Mg2+) and organic (nifedipine) Ca2+ channel antagonists and enhanced by the Ca2+ channel activator Bay-K-8644, it seems clear that Ca2+ gains access to the chromaffin cell cytosol mainly through specific voltage-dependent Ca2+ channels. Ca2+ uptake evoked by 59 mM K+ was linear during the first 5 s of stimulation and continued to rise at a much slower rate up to 60 s. The rate of Ca2+ entry became steeper as the external [Ca2+] increased; initial rates of Ca2+ uptake varied from 0.06 fmol/cells . s at 0.125 mM Ca2+ to 2.85 fmol/cell . s at 7.5 mM Ca2+. The early 90Sr2+ uptake was linear but faster than Ca2+ uptake and later on was also saturated; 133Ba2+ was taken up still at a much faster rate and was linear for the entire depolarization period (2-60 s). Increased [K+] gradually depolarized chromaffin cells; Ca2+ and Sr2+ uptakes were not apparent below 30 mM K+ but were linear for 30 to 60 mM K+. In contrast, substantial Ba2+ uptake was seen even in K+-free solutions; and in 5.9 mM K+, Ba2+ uptake was as high as Ca2+ uptake obtained in 60 mM K+. Five to ten-second pulses of 45Ca2+, 90Sr2+, or 133Ba2+ given at different times after pre-depolarization of chromaffin cells served to analyze the kinetics of inactivation of the rates of entry of each divalent cation. Inactivation of Ca2+ uptake was faster than Sr2+, and Ba2+ uptake inactivated very little. Neither voltage changes nor Ca2+ ions passing through the channels seems to cause their inactivation; however, experiments aimed to manipulate the levels of internal Ca2+ using the cell-permeable chelator Quin-2 or the ionophore A23187 strongly suggest that intracellular Ca2+ levels determine the rates of inactivation of these channels.