Serological recognition of HLA-DR allodeterminant corresponding to DNA sequence involved in gene conversion

HLA class 11 molecules were isolated from mouse L cells transfected with a DR gene and an allele, 52a, of locus DR III from an HLA-homozygous cell line, AVL, of the DR3 haplotype. The isolated molecules were found to possess a new allospecificity, named TR81. This specificity behaved allelic to the previously described DR III locus. The TR81 specificity was also present on the DR I gene product of the DR3 haplotype. The nucleotide sequence of the gene encoding TR81 differs from TR81-negative DR genes of the DRw52 family in only two codons, both located in the regions known to be involved in a gene conversion event. Consequently, the following conclusions can be formulated. (a) TR81 is a bi-locus specificity and allelic to TR22 only in its DR III locus localization. (b) The TR81 specificity is the phenotypic counterpart of the gene conversion event which led to the generation of the DR I gene of the DR3 haplotype. (c) One or both individual amino acid substitutions in the first domain of the DR chain are responsible for the TR81 allospecificity. (d) Since TR81 is expressed on the DR I chain of the DR3 haplotype, it is possible that TR81 and DR3 represent the same serological specificity.     

Effects of phosphorylation, MgATP, and ionic strength on the rates of papain degradation of heavy and light chains of smooth muscle heavy meromyosin at the S1-S2 junction

The effects of ionic strength, MgATP, and phosphorylation on the degradation rates of heavy meromyosin (HMM) by papain have been compared to their effects on the sedimentation coefficient (s20,w) to determine the relationship of the degradation rate to the equilibrium between the flexed and the extended forms (Suzuki, H., Stafford, W. F., Slayter, H. S., and Seidel, J. C. (1985) J. Biol. Chem. 260, 14810-14817). At 0.025 M NaCl, where HMM is predominantly in the flexed form, MgATP, Mg-adenylyl imidodiphosphate or MgADP reduce kH by 80-90%. MgATP exerts its optimal effect at this ionic strength, where at least 70% of HMM is flexed in the presence or absence of MgATP, suggesting that nucleotides reduce kH by decreasing the proteolytic susceptibility of the flexed form. At 0.5 M NaCl, where HMM is in the extended form, MgATP has no effect on kH. At low ionic strengths phosphorylation decreases kH but increases it in the presence of MgATP. Plots of kH against s20,w determined at various ionic strengths are linear, the data for phosphorylated and dephosphorylated HMM falling on the same line. Thus, raising the ionic strength or phosphorylating the 20-kDa light chain appears to alter kH by increasing the fraction of HMM in the extended form. The degradation rate of the 20-kDa light chain (kL) of dephosphorylated HMM responds to changes in ionic strength in essentially the same way as does kH, suggesting that the response of kL to changes in ionic strength can also be attributed to conversion of HMM to the extended form. However, kL for phosphorylated HMM measured in the presence of MgATP exhibits very little dependence on ionic strength.     

Electrogenic behavior of the human red cell Ca2+ pump revealed by disulfonic stilbenes

Summary A systematic study was made of the action of 4-acetamido-4-isothiocyanostilbene-2,2-disulfonic acid (SITS) and 4,4-diisothiocyanostilbene-2,2-disulfonic acid (DIDS) on active Ca²⁺ transport of human erythrocytes. Pumping activity was estimated in inside-out vesicles (IOV's) by means of Ca²⁺-selective electrodes or use of tracer⁴⁵Ca²⁺. The stilbenes exhibited an approximately equal inhibitory potency and their action could be overcome by carbonyl cyanidep-trifluoromethoxyphenylhydrazone (FCCP) at low but not at high stilbene concentrations. In the absence of DIDS. Ca²⁺ transport was not affected upon addition of valinomycin, but it was appreciably reduced when vesicles were preincubated with low DIDS concentrations. Such an effect was strictly dependent on the external K⁺ concentration and it was abolished when valinomycin was added together with FCCP. Similar results were obtained using IOV's prepared from intact cells which had been previously exposed to the stilbene. The findings clearly demonstrate the presence in human red cells of a partially electrogenic Ca²⁺ pump, exchanging one Ca²⁺ ion for one proton.     

Phosphate sequestration by glycerol and its effects on photosynthetic carbon assimilation by leaves

Glycerol induced a limitation on photosynthetic carbon assimilation by phosphate when supplied to leaves of barley (Hordeum vulgare L.) and spinach (Spinacia oleracea L.). This limitation by phosphate was evidenced by (i) reversibility of the inhibition of photosynthesis by glycerol by feeding orthophosphate (ii) a decrease in light-saturated rates of photosynthesis and saturation at a lower irradiance, (iii) the promotion of oscillations in photosynthetic CO₂ assimilation and in chlorophyll fluorescence, (iv) decreases in the pools of hexose monophosphates and triose phosphates and increases in the ratio of glycerate-3-phosphate to triose phosphate, (v) decreased photochemical quenching of chlorophyll fluorescence, and increased non-photochemical quenching, specifically of the component which relaxed rapidly, indicating that thylakoid energisation had increased. In barley there was a massive accumulation of glycerol-3-phosphate and an increase in the period of the oscillations, but in spinach the accumulation of glycerol-3-phosphate was comparatively slight. The mechanism(s) by which glycerol feeding affects photosynthetic carbon assimilation are discussed in the light of these results.Abbreviations Chl chlorophyll - C _i intercellular concentration of CO₂ - P phosphate - PGA glycerate-3-phosphate - Pi orthophosphate - triose-P sum of glyceraldehyde-3-phosphate and dihydroxyacetone phosphate     

Limitation of photosynthesis by changes in temperature

The aim of this work was to examine the effect of abrupt changes in temperature in the range 5 to 30°C upon the rate of photosynthetic carbon assimilation in leaves of barley (Hordeum vulgare L.). Measurement of the CO₂-assimilation rate in relation to the intercellular partial pressure of CO₂ at different temperatures and O₂ concentrations and at saturating irradiance showed that as the temperature was decreased photosynthesis was saturated at progressively lower CO₂ partial pressures and that the transition between the CO₂-limited and ribulose-1,5-bisphosphate-regeneration-limited rate became more abrupt. Feeding of orthophosphate to leaves resulted in an increased rate of CO₂ assimilation at lower temperatures at around ambient or higher CO₂ partial pressures both in 20% O₂ and in 2% O₂ and it removed the abruptness in the transition between the CO₂-limited and ribulose-1,5-bisphosphate-regeneration-limited rates. Phosphate feeding tended to inhibit carbon assimilation at higher temperatures. The response of carbon assimilation to temperature was altered by feeding orthophosphate, by changing the concentrations of CO₂ or of O₂ or by leaving plants in the dark at 4°C for several hours. Similarly, the response of carbon assimilation to phosphate feeding or to changes in 2% O₂ was altered by leaving the plants in the dark at 4°C. The mechanism of limitation of photosynthesis by an abrupt lowering of temperature is discussed in the light of the results.Abbreviations A rate of CO₂ assimilation - P _i intercellular partial pressure of CO₂ - RuBP ribulose-1,5-bisphosphate     

Alarm reaction and alert state inGambusia Affinis (Pisces,Poeciliidae) in response to chemical stimuli from injured conspecifics

We studied the behavior of the Poeciliid fishGambusia affinis after the introduction of 3 substances into their tank: a homogenization ofGambusia affinis, a homogenization of the Anabantid fishBetta splendens, and a blank made of distilled water. The response of the fish was measured as a change in their spatial distribution in the tank after the introduction of the substance. Two sizes of fish were used, and theGambusia homogenization produced clear alarm reactions in both, the fish fleeing to the bottom of the tank. This is one of a few examples available of recognition of alarm substances in non-ostariophysian fish. In addition, we found that the small fishes that had recently been exposed to the alarm substance stayed in an ‘alert state’, in which they had an increased sensitivity to mechanical and visual fright stimuli.     

A novel class of ammonium assimilation mutants of the photosynthetic bacterium Rhodobacter capsulatus

Nitrogen assimilation in Rhodobacter capsulatus has been shown to proceed via the coupled action of glutamine synthetase (GS) and glutamate synthase (GOGAT) with no measurable glutamate dehydrogenase (GDH) present. We have recently isolated a novel class of mutants of R. capsulatus strain B100 that lacks a detectable GOGAT activity but is able to grow at wild type rates under nitrogen-fixing conditions. While NH ₄ ⁺ -supported growth in the mutants was normal under anaerobic/photosynthetic conditions, the growth rate was decreased under aerobic conditions. Ammonium and methylammonium uptake experiments indicated that there was a clear difference in the ammonium assimilatory capabilities in these mutants under aerobic versus anaerobic growth. Regulation of expression of a nifH : : lacZ fusion in these mutants was not impaired. The possible existence of alternative ammonium assimilatory pathways is discussed.     

Social stimuli fail to act as entraining agents of circadian rhythms in the golden hamster

Summary The ability of social stimuli to act as entraining agents of circadian rhythms was investigated in golden hamsters (Mesocricetus auratus). In a first experiment, pairs of male hamsters (one of them enucleated and the other intact) were maintained under a light-dark (LD) cycle with a period of 23.3 h. Running-wheel activity was recorded to determine the effect of social interaction on the free-running circadian rhythm of activity. In several pairs, general activity and body temperature were also recorded. In all pairs the intact animals entrained to the LD cycle, whereas the activity rhythms of the enucleated animals free-ran with periods of approximately 24 h and showed no apparent sign of synchronization or relative coordination with the other member of the pair. In a second experiment, male hamsters maintained in constant darkness received pulses of social interaction, which have been reported to induce phase shifts of the activity rhythm. Consistent phase shifts in the running-wheel activity rhythm were not induced by the social pulses in our experiment. These results suggest strongly that social stimuli are not effective entraining agents of circadian rhythms in the golden hamster.Abbreviations CT circadian time - LD light-dark