RESUMEN
Plant cells are continuously exposed to environmental stresses such as hyper-osmolarity, and have to respond in order to survive. When 32P-labelled Chlamydomonas moewusii cells were challenged with NaCl, the formation of a new radiolabelled phospholipid was stimulated, which was barely detectable before stimulation. The phospholipid was identified as lyso-phosphatidic acid (LPA), and was the only lyso-phospholipid to be accumulated. The increase in LPA was dose- and time-dependent. When other osmotically active compounds were used, the formation of LPA was also induced with similar kinetics, although salts were better inducers than non-salts. At least part of the LPA was generated by phospholipase A2 (PLA2) hydrolysing phosphatidic acid (PA). This claim is based on PA formation preceding LPA production, and PLA2 inhibitors decreasing the accumulation of LPA and promoting the conversion of PA to diacylglycerol pyrophosphate. The latter is another metabolic derivative of PA that is implicated in cell signalling. The involvement of multiple lipid-signalling pathways in hyperosmotic stress responses is discussed.
Asunto(s)
Chlamydomonas/metabolismo , Lisofosfolípidos/biosíntesis , Fosfolipasas A/metabolismo , Animales , Chlamydomonas/enzimología , Clorpromazina/farmacología , Cromatografía en Capa Delgada , Frío , Activación Enzimática , Inhibidores Enzimáticos/farmacología , Calor , Luz , Lisofosfolípidos/metabolismo , Presión Osmótica , Ácidos Fosfatidicos/biosíntesis , Ácidos Fosfatidicos/metabolismo , Fosfolipasas A/antagonistas & inhibidores , Fosfolipasas A2 , Cloruro de Sodio/farmacologíaRESUMEN
The fatty acid and polar lipid compositions of the unicellular green alga Chlamydomonas moewusii were characterized. Since this organism is an important plant model for phospholipid-based signal transduction, interest was focused on the lipids phosphatidic acid, phosphatidylinositolphosphate and phosphatidylinositolbisphosphate. A phosphatidylinositol:phosphatidylinositolphosphate: phosphatidylinositolbisphosphate ratio of 100:1.7:1.3 was found. The polyphosphoinositides accounted for 0.8 mol% of the total phospholipids and their fatty acid compositions were similar to that of phosphatidylinositol except for the enrichment of linolenic acid in phosphatidylinositol phosphate. Phosphatidic acid accounted for 0.67 mol% of the phospholipids. Major structural glycerolipids were monogalactosyldiacylglycerol (35 mol%), digalactosyldiacylglycerol (15 mol%), sulfoquinovosyldiacylglycerol (10 mol%), diacylglyceryltrimethylhomoserine (16 mol%), phosphatidylglycerol (9 mol%), phosphatidylethanolamine (8 mol%) and phosphatidylinositol (6 mol%). Relative changes in the total fatty acid compositions found during growth on nutrient-limited medium reflected mainly alterations in the compositions of the chloroplast lipids phosphatidylglycerol and monogalactosyldiacylglycerol. [32P]Pi-incorporation studies revealed that it took 6 days before the amount of label in the major phospholipids was proportional to their abundance.
Asunto(s)
Chlamydomonas/metabolismo , Glicéridos/biosíntesis , Fosfolípidos/biosíntesis , Animales , Chlamydomonas/química , Glicéridos/química , Glicéridos/aislamiento & purificación , Cinética , Fosfatos/metabolismo , Fosfolípidos/química , Fosfolípidos/aislamiento & purificación , Radioisótopos de FósforoRESUMEN
The human, bovine, murine and rat interferon (IFN)-alpha families contain 4 conserved cysteines located at positions 1, 29, 99 and 139 that are involved in disulfide bridges. Rat and murine IFN-alpha subspecies carry a fifth Cys (Cys-86) which is not conserved in bovine and human IFN-alpha subspecies except for human IFN-alpha 1. Changing Cys-86 in rat IFN-alpha 1 into Ser or Tyr virtually abolished antiviral activity. As shown by others, the substitution of Cys-86 to Ser in human IFN-alpha 1 had no pronounced effect on activity. This suggests that in contrast to human and bovine IFN-alpha, Cys-86 in rodent IFN-alpha plays a crucial role in receptor binding. Changing Cys-1 to Gly in rat IFN-alpha 1 also destroyed activity, in agreement with results obtained in the human IFN-alpha 1 system.