Molecular alteration of a muscarinic acetylcholine receptor system during synaptogenesis

Biochemical properties of the muscarinic acetylcholine receptor system of the avian retina were found to change during the period when synapses form in ovo. Comparison of ligand binding to membranes obtained before and after synaptogenesis showed a significant increase in the affinity, but not proportion, of the high affinity agonist-binding state. There was no change in receptor sensitivity to antagonists during this period. Pirenzepine binding, which can discriminate muscarinic receptor subtypes, showed the presence of a single population of low affinity sites (M2) before and after synaptogenesis. The change in agonist binding was not due to the late development of receptor function; tests for receptor-stimulated phosphatidylinositol turnover and for modulation of agonist binding by guanylylimidodiphosphate showed functional coupling to be present several days prior to the onset of synapse formation. However, detergent-solubilization of membranes eliminated differences in agonist binding between receptors from embryos and hatched chicks, suggesting a developmental change in interactions of the receptor with functionally related membrane components. A possible basis for altered interactions was obtained from isoelectric point data showing that the muscarinic receptor population underwent a transition from a predominantly low pI form (4.25) in 13 day embryos to a predominantly high pI form (4.50) in newly hatched chicks. The possibility that biochemical changes in the muscarinic receptor play a role in differentiation of the system by controlling receptor position on the surface of nerve cells is discussed.     

A numerical taxonomic study of Flavobacterium-Cytophaga strains from dairy sources

Phenotypic data on 203 Gram-negative non-fermentative bacteria of the Flavobacterium-Cytophaga group isolated from milk and butter were analyzed by numerical taxonomic techniques. Twenty reference strains including species of Flavobacterium, Cytophaga and strains of Pseudomonas paucimobilis were included in the study. Using the matching coefficient of Sokal & Michener with antibiotic susceptibility data included, 139 isolates were recovered in nine clusters. Six of these clusters were linked at or above the 85% S level while three were linked at or above the 79% S level. The largest cluster, representing 46.3% of the isolates, could be equated with Flavobacterium sp. Group IIb. Other clusters could be equated with Flavobacterium sp. L 16/1 (22.7% of isolates), F. balustinum (10.8% of isolates), F. breve (4.4%), F. multivorum (3.5%) and Cytophaga johnsonae (1.5%). The cluster resembling Flavobacterium sp. L 16/1 and a smaller unclassified cluster, were exceptional in being susceptible to the antibiotics cephalothin and penicillin G.     

The synergistic effect of carbon concentration and high temperature on lipid peroxidation in Peridinium gatunense

Lipid peroxidation in Peridinium samples taken from two differentdepths in Lake Kinneret fluctuated throughout the spring withan overall increasing trend. Samples from 0.5 and 5 m showeda similar peroxidation pattern, which was maximal after thefall off in algal biomass. The rapid decline in Peridinium biomasscoincided with ambient lake temperatures of 21–23C. Fattyacid composition profiles were similar at both depths, althoughafter the peak of the bloom, a significant increase in polyunsaturatedfatty acids and oleic acid was only found at 0.5 m, togetherwith a decrease in the percentage of polyunsaturated fatty acids.These effects were related to ambient light stress rather thana result of lipid peroxidation. Lake samples taken at differentperiods of the bloom and incubated at various temperatures showeddifferential peroxidation. Higher temperatures caused increasedlipid peroxidation, but this appeared to be dependent on thesampling period. Samples withdrawn from the lake at the beginningof the bloom showed little peroxidation after a 5 day incubationat 14C, room temperature (25C) or ambient lake temperature(16C) compared to mid-bloom samples in which there was a significantincrease in peroxidation when they were incubated at room temperature(25C) or ambient lake temperature (22C). Incubation at 14Cinhibited peroxidation; however, samples from mid-bloom againshowed enhanced peroxidation compared with those from the beginningof the bloom. These in situ results suggested a relationshipbetween temperature, another environmental variable during thebloom and lipid peroxidation in Peridinium. As total dissolvedinorganic carbon (DIC) concentrations fall significantly duringthe progress of the bloom and represent an important sourceof environmental stress, laboratory experiments were establishedto investigate the synergistic effect of temperature and carbonnutrition on lipid peroxidation in Peridinium cultures. Increasedtemperature alone caused a slight increase in lipid peroxidation,but this was greatly augmented by carbon limitation. Althoughcarbon limitation induced increased catalase activity, at highertemperatures activity declined after 48 h, allowing for thesubstantial increase in lipid peroxidation.