Inhibition of phospholipid methyltransferase during zymosan induced secretion of platelet-activating factor in human polymorphonuclear leukocytes

Phagocytosis of zymosan particles coated with complement induces a time and dose dependent inhibition of the enzyme phospholipid methyltransferase in human polymorphonuclear cells. The extent of phospholipid methyltransferase inhibition induced by various concentrations of zymosan strongly correlates with the secretory process: liberation of platelet-activating factor (PAF) and β-glucuronidase. Zymosan also decreases the incorporation of ³H-methyl group into phospholipids in cells pre-labeled with (³H-methyl)-methionine. Finally, preincubation of cells with 3-deaza-adenosine and homocysteine thiolactone, inhibitors of phospholipid methyltransferase, decrease the incorporation of ³H-methyl group into phospholipids in cells pre-labeled with (³H-methyl)-methionine and modulate the release of PAF. These results suggest that phospholipid methylation plays an important role during the transduction of the secretory signal triggered by zymosan in human polymorphonuclear cells.     

Isolation of a mitochondrial factor from rat liver which potentiates the inactivation of glutamate dehydrogenase by lysosomes

Rat liver glutamate dehydrogenase (L-glutamate: NAD(P) oxidoreductase, deaminating) E.C. 1.4.1.3.) is inactivated by the mitochondrial matrix in combination with lysosomal preparations. Neither lysosomal or mitochondrial matrix extracts per se inactivate the enzyme appreciably under the conditions used. Fractionation of the matrix indicates that a low molecular weight factor is responsible for the potentiation of inactivation of glutamate dehydrogenase by lysosomes. Its absorption spectrum and chromatographic behaviour suggest that this factor is NADP.     

The effect of metals on isolated pea pyruvate decarboxylase

Pyruvate decarboxylase (PDC) was prepared from four-day-old pea seedlings by a procedure which involves extraction of plant material with a phosphate buffer, fractionation of the extract with ammonium sulphate, desalting by dialysis or gel filtration on Sephadex G-25 column, chromatography on DEAE cellulose and filtration on Sepharose 4B. The PDC preparation activity 10 000 U g^-1 protein was about 600 fold higher than that of the sodium phosphate buffer extract. According to the enzyme behaviour during the gel filtration on different carriers the molecular mass of pea PDS was estimated at about 10⁶. Magnesium ions and thiamine pyrophosphate were found to be coenzymes of PDC. Cofactors can be removed by 48 h dialysis followed by chromatography on DEAE cellulose. Apoenzym is activated optimally with the concentration of cofactors of 0.002 M. Magnesium ions can be replaced in their activation function by ions of Fe²⁺, Ni²⁺, Co²⁺, Zn²⁺ and Mn²⁺. Another ions,i.e. Ba²⁺, Ca²⁺, Cd²⁺, Hg²⁺ and Cu²⁺ are inactive. Assumption about the relation between the ion diameter and degree of activation is formulated.     

Additional data on complex inclusions evoked by wisteria vein mosaic virus in pea leaf cells

Large complex inclusions evoked by wisteria vein mosaic virus contain cylindrical inclusions, mostly pinwheels (and bundles) and rarely also scrolls and laminar inclusions. Bundles are often abutted to cell walls at plasmodesmata and show association with endoplasmic reticulum and cisternae. Virus aggregates are attached to cylindrical inclusions, various membranes and/or plasmalemma. Cytoplasm contains more or less disintegrated chloroplasts and mitochondria, abnormal membranes, many ribosomes, bounded vesicles with fibrillar contents, numerous and large microbodies, and membranous whorls. These phenomena are not specific.     

Some effects of the induction of gametogenesis in the populations of the homothallic algaChlamydomonas geitleri Ettl

The induction of gametogenesis in the studied homothallic alga by the transfer to a nitrogen-Less medium leads to an adaptation of the cell population until a dynamic equilibrium is attained. Throughout the adaptation, the homeostatic forces regulating the number of the cells in the population assert themselves on the basis of internal nitrogen circulation. Part of the induced cells which perform no conjugation is probably destroyed by lysing, whereas the cells being just in the pre-Induction phase as well as those having passed the phase without being induced to gametes, continue their cycles by means of the released nitrogenous substances. The conditions which in some cells cause the induction of gametogenesis, produce a partial spontaneous synchronisation in other cells. The course of the cell cycles in parts of the culture may be determined according to the pulses of the increasing number of the zygotes within the whole cell population, if the cell cycles have run at a certain degree of synchrony. The culture conditions which induce gametogenesis cause a quick decrease of the biosyntheses of the RNAs while the biosyntheses of the DNAs are almost maintained at the original level. During the dynamic equilibrium of the population, the average content of the RNAs per cell remains very low, whereas the average content of the DNAs per cell virtually does not change (compared with the original state).