Myristyl and palmityl acylation of pI 5.1 carboxylesterase from porcine intestine and liver.

Immunoblotting analyses revealed the presence of carboxylesterase in the porcine small intestine, liver, submaxillary and parotid glands, kidney cortex, lungs and cerebral cortex. In the intestinal mucosa, the pI 5.1 enzyme was detected in several subcellular fractions including the microvillar fraction. Both fatty monoacylated and diacylated monomeric (F1), trimeric (F3) and tetrameric (F4) forms of the intestinal protein were purified here for the first time by performing hydrophobic chromatography and gel filtration. The molecular mass of these three enzymatic forms was estimated to be 60, 180 and 240 kDa, respectively, based on size-exclusion chromatography and SDS/PAGE analysis. The existence of a covalent attachment linking palmitate and myristate to porcine intestinal carboxylesterase (PICE), which was suggested by the results of gas-liquid chromatography (GLC) experiments in which the fatty acids resulting from alkali treatment of the protein forms were isolated, was confirmed here by the fact that [3H]palmitic and [3H]myristic acids were incorporated into porcine enterocytes and hepatocytes in cell primary cultures. Besides these two main fatty acids, the presence of oleic, stearic, and arachidonic acids was also detected by GLC and further confirmed by performing radioactivity counts on the 3H-labelled PICE forms after an immunoprecipitation procedure using specific polyclonal antibodies, followed by a SDS/PAGE separation step. Unlike the F1 and F4 forms, which were both myristoylated and palmitoylated, the F3 form was only palmitoylated. The monomeric, trimeric and tetrameric forms of PICE were all able to hydrolyse short chain fatty acids containing glycerides, as well as phorbol esters. The broad specificity of fatty acylated carboxylesterase is discussed in terms of its possible involvement in the metabolism of ester-containing xenobiotics and signal transduction.     

Péétration et migration d'éléments minéraux appliqués sur les feuilles en présence de diméthylsulfoxyde

The aim of this work was to determine the effect of DMSO on the uptake and translocation of potassium and phosphorus applied on corn and bean leaves. Radioactive isotopes ⁴²K and ³²P were used in most of the experiments. The results obtained reveal that DMSO (0.5% and above) increases the penetration of potassium applied as nitrate or chloride, but seems to have no effect on the penetration of ³²P when applied as different phosphates.     

Modelling phytoplankton development in whole drainage networks: the RIVERSTRAHLER Model applied to the Seine river system

Phytoplankton development in river systems is under the control of various meteorological, hydrological, chemical and biological factors. Because of the continuity of the aquatic systems which progress from headwaters to the largest rivers, the interplay of these control factors can only be understood at the scale of the entire drainage network. The RIVERSTRAHLER Model, based on the concept of stream-order, has been established for that purpose. It has been applied here on two rivers from the Seine basin: rivers Marne and Oise. It is shown that hydrological factors determine the time of onset, and the position within the drainage network, of the spring algal bloom. Phosphorus availability, when limiting, controls the intensity of the bloom. During summer, top-down control, linked to grazing and other causes of mortality, has a marked impact on algal dynamics.