Farnesylcysteine analogues inhibit chemotactic peptide receptor-mediated G-protein activation in human HL-60 granulocyte membranes

Analogues of S-prenylated cysteine like N-acetyl-S-trans,trans-farnesyl-L-cysteine (AFC) have previously been shown to inhibit the carboxyl methylation of proteins carrying a C-terminal S-prenylated cysteine residue and to block the endotoxin-activated serum-elicited chemotactic response of mouse macrophages. Here, we show that AFC inhibits both basal and formyl peptide receptor-stimulated binding of guanosine 5'-O-(3-thiotriphosphate) (GTP[S]) to and hydrolysis of GTP by membranes of myeloid differentiated HL-60 granulocytes. Receptor-stimulated GTP[S] binding and GTP hydrolysis are more sensitive to AFC inhibition than basal G-protein functions. Inhibition of formyl peptide receptor-mediated G-protein activation is also observed for S-trans,trans-farnesyl-3-thiopropionic acid, but not for N-acetyl-S-trans-geranyl-L-cysteine, N-acetyl-L-cysteine, or the methyl ester of AFC, suggesting that the farnesyl moiety and the carboxyl group, but not the peptide bond of AFC are required for inhibition. The observations that exogeneous S-adenosyl-L-methionine is apparently not required for and S-adenosyl-L-homocysteine does not attenuate the inhibitory action of AFC raise the distinct possibility that AFC inhibits receptor-mediated G-protein interaction by a mechanism other than inhibition of protein carboxyl methylation.

[Clinico-neurologic and neurophysiologic findings in hemophilic boys and their effect on social integration]

Prophylactic substitution of severe (sometimes even moderate) haemophilia (home self-treatment) has, besides other measures, not only had a positive effect on the findings in the joints but also on the danger of bleeding in the CNS. The injuries of the head in haemophiliacs are analysed and the social integration is shown (school, occupation, spare-time planning). Compared with previous information in literature the high incidence of pathological EEG findings has decreased. Without observing clinically perceptible deficits, the acoustically evoked brain stem potentials were often found to be altered.

Isozyme-selective stimulation of phospholipase C-beta 2 by G protein beta gamma-subunits

Hydrolysis by phospholipase C (PLC) of phosphatidylinositol 4,5-bisphosphate is a key mechanism by which many extracellular signalling molecules regulate functions of their target cells. At least eight distinct isozymes of PLC are recognized in mammalian cells. Receptor-controlled PLC is often regulated by G proteins, which can be modified by pertussis toxin in some cells but not in others. In the latter cells, PLC-beta 1, but not PLC-gamma 1 or PLC-delta 1, may be activated by members of the alpha q-subfamily of the G protein alpha-subunits. An unidentified PLC in soluble fractions of cultured human HL-60 granulocytes is specifically stimulated by G protein beta gamma subunits purified from retina and brain. Identification of a second PLC-beta complementary DNA (PLC-beta 2) in an HL-60 cell cDNA library prompted us to investigate the effect of purified G protein beta gamma subunits on the activities of PLC-beta 1 and PLC-beta 2 transiently expressed in cultured mammalian cells. We report here that PLC-beta 1 and PLC-beta 2 were stimulated by free beta gamma subunits and that PLC-beta 2 was the most sensitive to beta gamma stimulation. Thus stimulation of PLC by beta gamma subunits is isozyme-selective and PLC-beta 2 is a prime target of beta gamma stimulation. Activation of PLC-beta 2 by beta gamma subunits may be an important mechanism by which pertussis toxin-sensitive G proteins stimulate PLC.

Proteolysis in Euglena gracilis : II. Soluble and particle-bound acidic proteinase activities of the cysteine and aspartic types during growth and chloroplast development

Endoproteolytic activities (EC 3.4.22. and 23.) of cell-free extracts of Euglena gracilis, measured by autolysis and azocaseinolysis, vary considerably during the culture growth cycle. They are high in the lag phase, drop sharply up to the mid-logarithmic phase, and then rise again reaching the initial high levels in the stationary phase. This pattern has been observed for both the soluble and the particulate proteolytic activities of four cell types differing with regard to the developmental state of the chloroplast: dark-grown, light-induced, and light-grown wild-type cells, as well as light-grown apoplastic W3BUL mutant cells, all on a glucose-based medium. Therefore, the activity of the main intracellular proteinases is neither directly nor indirectly light-regulated, but seems to be controlled by the availability of nutrients. Endogenous inhibitors of proteinases could not be detected. Cysteine proteinase activity has been found in the soluble and the particulate fractions, but aspartic proteinase activity in the latter ones only. Different cysteine proteinases may be present in the two fractions, during the different growth phases, and in the four cell types studied.

Coomassie brilliant blue G-250 dye-binding technique for determination of autolytic protein breakdown in Euglena gracilis and comparison to other methods of autolysis measurement

The Coomassie brilliant blue G-250 dye-binding technique of M. M. Bradford (1976, Anal. Biochem. 72, 248-254) for protein quantification has been used to measure autolytic protein breakdown in cell-free extracts of Euglena gracilis. Specific autolysis rates were calculated from the difference between initial and actual absorbances at different incubation times of Coomassie brilliant blue-stained protein. They were found to depend linearly on time and initial protein concentration. Calibration against another method of protein determination is necessary due to different color yields with various protein mixtures. The high sensitivity and reproducibility of this method permit determination of specific autolysis rates below 0.1% mg-1 h-1 over a pH range between 3 and 8, without protein precipitation or pH adjustment, and in the presence of high amounts of amino acids and/or small peptides. Results obtained by this method are comparable to those of other autolysis measurements and to proteolytic activity determination by azocaseinolysis. Proteolytic autolysis has been observed in both the soluble and the particulate fractions of E. gracilis cell-free extracts, but displays different pH optima and specific activities in these fractions, as is also the case for azocaseinolysis. The method described is easy to perform, inexpensive, time saving, and should be applicable to other biological systems as well.

Dark-induced chloroplast dedifferentiation in Euglena gracilis

Transfer of light-grown autotrophic Euglena gracilis cells to darkness and carbon (glucose) containing heterotrophic media causes structural and functional decomposition of the photosynthetic apparatus. The process can be ascribed to a strict diluting-out mechanism of stroma constituents among the progeny, as shown for ribulose-1,5-bisphosphate carboxylase (RuBPCase, EC 4.1.1.39), and aminoacyl-tRNA synthetases (Aa-RS; especially Leu-RS, EC 6.1.1.4) activities. The diluting-out effect of thylakoid membranes and chlorophyll seems to be superimposed by additional degradations, beginning soon after the transfer of cells to darkness. Cultivation of cells in darkness in 0.03 M KCl or without utilizable organic carbon (resting media) preserves chloroplast structure and function over a long period, indicating negligible turnover in these cells. Thus, under both growing and resting conditions, darkness induces the arrest of synthesis of plastid constituents. Experiments with the inhibitors cycloheximide, chloramphenicol, and nalidixic acid demonstrate that chloroplast dedifferentiation does not require organelle gene expression, but it is more strictly dependent on biosynthetic events in the nucleo-cytoplasmic compartment than the reverse process, light-induced chloroplast formation. Since cycloheximide at low concentrations in growth medium causes a marked suppression of precursor uptake or re-utilization similar to that in cells of resting media, intracellular precursor deficiency is suggested to control the observed blockade in cytoplasmic synthesis of plastid proteins. On the other hand, darkness might signalize the stop of gene expression in the organelles.