Phospholipase C in Dictyostelium discoideum:Cyclic AMP surface receptor and G-protein-regulated activity in vitro

The cellular slime mould Dictyostelium discoideum shows several responses after stimulation with the chemoattractant cAMP, including a transient rise in cyclic AMP (cAMP), cGMP and Ins(1,4,5)P-3. In this paper the regulation of phospholipase C in vitro is described. Under our experimental conditions commercial PtdIns(4,5)P-2 cannot be used to analyse phospholipase C activity in Dictyostelium lysates, because it is hydrolysed mainly to glycerophosphoinositol instead of Ins(l,4,5)P-3. Enzyme activity was determined with endogenous unlabelled PtdInsP(2) as a substrate. The product was measured by isotope-dilution assay and identified as authentic Ins(1,4,5)P-3. Since phospholipase C is strictly Ca2+-dependent, with an optimal concentration range of 1-100 mu M, cell lysates were prepared in EGTA and the enzyme reaction was started by adding 10 mu M free Ca2+. Phospholipase C activity increased 2-fold during Dictyoslelium development up to 8 h of starvation, after which the activity declined to less than 10 % of the vegetative level. Enzyme activity in vitro increased up to 2-fold after stimulation of cells with the agonist cAMP in vivo. Addition of 10 mu M guanosine 5'-[gamma-thio]triphosphate during lysis activated the enzyme to the same extent, and this effect was antagonized by guanosine 5'-[beta-thio]diphosphate. These results strongly suggest that surface cAMP receptors and G-proteins regulate phospholipase C during Dictyostelium development.</p

Density functional approach to study structural properties and Electric Field Gradients in rare earth materials

We investigated the effect of spin polarization on the structural properties and gradient of electric field (EFG) on Sn, In, and Cd impurity in RSn$_3$ (R=Sm, Eu, Gd) and RIn$_3$ (R=Tm, Yb, Lu) compounds. The calculations were performed self-consistently using the scalar-relativistic full potential linearized augmented plane wave method. The local density approximations (LDA) and generalized gradient approximation without spin polarization (GGA) and with spin polarization (GGA+SP) to density functional theory were applied. In addition to that we performed some calculations within open core treatment (GGA+open core). It is clearly seen that GGA+SP is successful in predicting the larger lattice parameter and the dramatic drop of EFG for R=(Eu, Yb) relative to other rare earth compounds. This is an indication that spin splitting generated by spin polarization without any modification, is capable of treating properly the highly correlated f electrons in these systems.Comment: 14 Pages, 3 Figures, 5 Table