Differential Regulation by Calmodulin of Basal, GTP-, and Dopamine-Stimulated Adenylate Cyclase Activities in Bovine Striatum

The concentration requirements of calmodulin in altering basal, GTP-, and dopamine-stimulated adenylate cyclase activities in an EGTA-washed particulate fraction from bovine striatum were examined. In the bovine striatal particulate fraction, calmodulin activated basal adenylate cyclase activity 3.5-fold, with an EC50 of 110 nM. Calmodulin also potentiated the activation of adenylate cyclase by GTP by decreasing the EC50 for GTP from 303 +/- 56 nM to 60 +/- 10 nM. Calmodulin did not alter the maximal response to GTP. The EC50 for calmodulin in potentiating the GTP response was only 11 nM as compared to 110 nM for activation of basal activity. Similarly, calmodulin increased the maximal stimulation of adenylate cyclase by dopamine by 50-60%. The EC50 for calmodulin in eliciting this response was 35 nM. These data demonstrate that calmodulin can both activate basal adenylate cyclase and potentiate adenylate cyclase activities that involve the activating GTP-binding protein, Ns. Mechanisms that involve potentiation of Ns-mediated effects are much more sensitive to calmodulin than is the activation of basal adenylate cyclase activity. Potentiation of GTP-stimulated adenylate cyclase activity by calmodulin was apparent at 3 and 5 mM MgCl2, but not at 1 or 10 mM MgCl2. These data further support a role for calmodulin in hormonal signalling and suggest that calmodulin can regulate cyclic AMP formation by more than one mechanism.     

Organization and structure of Volvox beta-tubulin genes

Summary Genomic clones encoding two Volvox -tubulin genes have been isolated and shown to represent the only two -tubulin genes in the genome. Restriction fragment length polymorphism analysis was used to demonstrate that the two genes are genetically linked. One of these genes was sequenced and the mRNA start site(s) determined by primer extension. A comparison of its sequence to those of the two -tubulin genes of Chlamydomonas revealed: (1) a high degree of conservation of the coding region, with the predicted amino acid sequence differing only in the C-terminal residue; (2) extensive sequence conservation in the 5 untranslated leader region and a 16 bp (putative regulatory) sequence in the promoter region; (3) the same number and location of introns, with a short region of homology in intron 1, but little significant homology in introns 2 and 3.     

Effects of simulated fire on vesicular-arbuscular mycorrhizae in pinyon-juniper woodland soil

Effects of fire on vesicular-arbuscular mycorrhizal fungi were tested using microcosms constructed from soil, litter, and duff collected beneath canopies of pinyon pine, Utah juniper, and in the open space (interspace). Burning was conducted over wet and dry soils. Soil temperatures were monitored continuously throughout the microcosms during burning. Plants grown in soils burned when dry had a lower VAM colonization than soils burned when wet. Juniper soils demonstrated the greatest reduction, over 95%, compared to their respective controls. Plants grown in interspace soils burned when wet were least affected. There was a positive correlation (r²=0.90) between the decrease in VAM colonization and the soil temperature as a result of the fire. Temperature effects, and associated reductions in VAM, were related to amount of litter burned in each microcosm and the moisture content of the soils.     

The in-vivo response of the ribulose-1,5-bisphosphate carboxylase activation state and the pool sizes of photosynthetic metabolites to elevated CO2 inPhaseolus vulgaris L.

The short-term, in-vivo response to elevated CO₂ of ribulose-1,5-bisphosphate carboxylase (RuBPCase, EC 4.1.1.39) activity, and the pool sizes of ribulose 1,5-bisphosphate, 3-phosphoglyceric acid, triose phosphates, fructose 1,6-bisphosphate, glucose 6-phosphate and fructose 6-phosphate in bean were studied. Increasing CO₂ from an ambient partial pressure of 360–1600 bar induced a substantial deactivation of RuBPCase at both saturating and subsaturating photon flux densities. Activation of RuBPCase declined for 30 min following the CO₂ increase. However, the rate of photosynthesis re-equilibrated within 6 min of the switch to high CO₂, indicating that RuBPCase activity did not limit photosynthesis at high CO₂. Following a return to low CO₂, RuBPCase activation increased to control levels within 10 min. The photosynthetic rate fell immediately after the return to low CO₂, and then increased in parallel with the increase in RuBPCase activation to the initial rate observed prior to the CO₂ increase. This indicated that RuBPCase activity limited photosynthesis while RuBPCase activation increased. Metabolite pools were temporarily affected during the first 10 min after either a CO₂ increase or decrease. However, they returned to their original level as the change in the activation state of RuBPCase neared completion. This result indicates that one role for changes in the activation state of RuBPCase is to regulate the pool sizes of photosynthetic intermediates.Abbreviations and symbols A net CO₂ assimilation rate - C_a ambient CO₂ partial pressure - C_i intercellular CO₂ partial pressure - CABP 2-carboxyarabinitol 1,5-bisphosphate - k_cat catalytic turnover rate per RuBPCase molecule - PFD photon flux density (400 to 700 nm on an area basis) - PGA 3-phosphoglyceric acid - P_i orthophosphate - RuBP ribulose 1,5-bisphosphate - RuBPCase ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39)     

Surface EMG recordings and pain-related disorders: A diagnostic framework

Surface electromyography provides a very valuable set of information when used diagnostically with pain-related disorders. Unfortunately, most researchers and clinicians limit their investigation to only one level of diagnostic information available concerning the neuromuscular system. This article develops and encourages the clinician/researcher to consider three levels of diagnostic information: emotional, organ-related, and postural aspects. The theoretical background and diagnostic procedures used to investigate each is presented. Differential treatment considerations, given differential diagnostic findings, are discussed.     

Persistence of community structure: what happens when you change taxonomic scale?

It is common in community ecology to use the species as the taxonomic category of interest, yet in rich tropical assemblages containing guilds of very similar species this may not be appropriate. Such assemblages may be organized at the level of guilds rather than at the finer species level. In a ten-year study of assemblages of fish at One Tree Reef, Great Barrier Reef, we found species composition and the number of fish on a given lagoonal patch reef vary greatly across time (Sale and Douglas 1984; Sale et al. in preparation). The mean average proportional similarity of a reef's assemblage to itself at different times (censuses) is usually low at a value of around 0.5. This apparent variability may be ecologically irrelevant noise if organization is at the higher guild level. We have recast our database at the guild level to test this possibility. Thirteen guilds were defined by the diets, foraging habitats and times of the individual species comprising them. Similarity of an assemblage to itself at successive censuses was re-calculated using the number of individuals in each guild instead of the numbers in each species. This analysis yielded significantly higher levels of similarity (P<0.01) among censuses. To test whether this increase in similarity was due solely to the smaller number of categories used to calculate the similarity indices, 5 sets of randomly generated guilds were constructed using a Monte Carlo approach. No significant difference (P>0.05) was found between the average similarity among censuses when assemblages were classified into these null guilds and when they were classified according to the real guilds. These results indicate that shifting to the larger taxonomic scale of guilds does not reveal a significantly more persistent assemblage structure than that revealed when analysis is at the smaller scale of species. There is no evidence of an underlying organization of these assemblages at the guild level.     

Amino acid substitution analysis of E. coli thymidylate synthase: The study of a highly conserved region at the N-terminus

Amino acid substitution analysis within a highly conserved region of Escherichia coli thymidylate synthase (TS), using suppression of amber mutations by tRNA suppressors, has yielded a bank of 124 new mutationally altered TS proteins. These mutant proteins have been used to study the structure-function relationship of the Escherichia coli TS protein at the N-terminus corresponding to residues 20 through 35. This region contains a block of amino acids whose sequence has been well conserved among other known TS proteins from various organisms. Positions 20 through 25 contain a surface loop structure and positions 26 through 35 encompass a β-strand. We find that residues surrounding a β-bulge structure within the β-strand are particularly sensitive to amino acid substitution, suggesting that this structure is maintained by a highly ordered packing arrangement. Three residues in the surface loop that are present at the base of the substrate binding pocket are also sensitive to amino acid substitution. The remainder of the conserved sites, including those at the dimer interface, are tolerant to most, if not all, of the substitutions tested. © 1992 Wiley-Liss, Inc.