Phospholipid turnover during phagocytosis in human polymorphonuclear leucocytes

We have previously observed that the phagocytosis of zymosan particles coated with complement by human polymorphonuclear leucocytes is accompanied by a time- and dose-dependent inhibition of phosphatidylcholine synthesis by transmethylation [García Gil, Alonso, Sánchez Crespo & Mato (1981) Biochem. Biophys. Res. Commun. 101, 740–748]. The present studies show that phosphatidylcholine synthesis by a cholinephosphotransferase reaction is enhanced, up to 3-fold, during phagocytosis by polymorphonuclear cells. This effect was tested by both measuring the incorporation of radioactivity into phosphatidylcholine in cells labelled with [Me-¹⁴C]choline, and by assaying the activity of CDP-choline:diacylglycerol cholinephosphotransferase. The time course of CDP-choline:diacylglycerol cholinephosphotransferase activation by zymosan mirrors the inhibition of phospholipid methyltransferase activity previously reported. The extent of incorporation of radioactivity into phosphatidylcholine induced by various doses of zymosan correlates with the physiological response of the cells to this stimulus. This effect was specific for phosphatidylcholine, and phosphatidyl-ethanolamine turnover was not affected by zymosan. The purpose of this enhanced phosphatidylcholine synthesis is not to provide phospholipid molecules rich in arachidonic acid. The present studies show that about 80% of the arachidonic acid generated in response to zymosan derives from phosphatidylinositol. A transient accumulation of arachidonoyldiacylglycerol has also been observed, which indicates that a phospholipase C is responsible, at least in part, for the generation of arachidonic acid. Finally, isobutylmethylxanthine and quinacrine, inhibitors of phosphatidylinositol turnover, inhibit both arachidonic acid generation and phagocytosis, indicating a function for this pathway during this process.     

Humirianthenolides,new degraded diterpenoids from Humirianthera rupestris

The tuber of Humirianthera rupestris (Icacinaceae) contains the degraded diterpenoids 3β,20-epoxy-30α- hydroxy- 14-oxo-9β-podocarpan-19,6β-olide (humirianthenolide A), 3β,20-epoxy-3α,14α-dihydroxy-9β-podocarpan-19,6β- olide (humirianthenolide B), 3β,20; 16,14-diepoxy-3α-hydroxy-17-nor-15-oxo-9β-abiet-13-en-19,6β-olide (humirianthenolide C), 3β,20-epoxy-3α,14-dihydroxy-13-oxo-9β-podocarp-8(14)-en-19,6β-olide (humirianthenolide D), 3β,20-epoxy-3α-hidroxy-14-oxo-8α,9β-podocarpan-19,6β-olide (humirianthenolide E) and 3β,20-epoxy-3α,14β- dihydroxy-8α,9β-podocarpan-19,6β-olide (humirianthenolide F). ¹H NMR and ¹³C NMR spectroscopy were efrective for the determination of the humirianthenolide structures.     

The use of azidoarylimidoesters in RNA-protein cross-linking studies with Escherichia coli ribosomes

A series of related hetero-bifunctional RNA-protein cross-linking reagents has been prepared, carrying an imidoester or N-hydroxysuccinimide ester function at one end of the molecule, and a phenylazido function at the other. These compounds have been applied to RNA-protein cross-linking studies with ribosomal subunits, and one of them, p-azido-phenylacetic imidoester, has proved to be a particularly useful reagent for this purpose. The reagent first reacts specifically with protein amino groups, and subsequent photolysis of the azide group leads to cross-linking to the RNA in yields of up to 8% of the total protein. The whole reaction takes place under very mild conditions in aqueous solution.The individual proteins concerned in the cross-links have been identified by two-dimensional gel electrophoresis, and the existence of a covalent cross-link was confirmed by the isolation by two different methods of protein-oligonucleotide complexes carrying a ³²P label. Although most of the ribosomal proteins could be cross-linked to their corresponding ribosomal RNA within the individual subunits, RNA-protein cross-links at the ribosomal subunit interface were only detectable in vanishingly small amounts.The advantages of this type of genuine hetero-bifunctional reagent in RNA-protein cross-linking studies are discussed.     

Dehydrodieugenols from Ocotea cymbarum

The trunk wood of Ocotea cymbarum from the Amazon basin contains α-phellandrene, α-pinene, eugenol, dehydrodieugenol and its monomethyl ether, as well as the previously unknown dehydrodieugenol-B (4,5′-diallyl-2′-hydroxy-2,3′-dimethoxydiphenyl ether).     

Role of H-2 antigens in the host response to methylcholanthrene-induced tumors

H-2 loss variant sublines of a sarcoma (M-AS), induced by methylcholanthrene in an (A × A.SW)F₁ mouse, were used to study the role of the MHC products in the recognition of MC-TSTA. The two reciprocal variant sublines (M-A and M-S) were found to express the TSTA of the original tumor as shown by cross-reactions in graft rejection experiments performed in (A × A.SW)F₁ mice. In the A/Sn and A.SW mice the presence of the reciprocal parental H-2 antigens on the immunizing cells decreased the response against the tumor antigens. An admixture of lymphocytes derived from hyperimmune mice inhibited the outgrowth of the tumor cells. The growth inhibition was mediated by T cells and was H-2 restricted. Cells derived from hyperimmune syngeneic mice inhibited the outgrowth of the variant subline used for immunization but had no effect on the reciprocal variant subline.     

Tyrosine transport by membrane vesicles isolated from rat brain

Tyrosine uptake by membrane vesicles derived from rat brain has been investigated. The uptake is dependent on an Na⁺ gradient ([$\text{Na}{}^{\mathrm{+}}\text{]}\text{outside}\text{> [}\text{Na}{}^{\mathrm{+}}\text{]}\text{inside}$). The uptake is transport into an osmotically active space and not a binding artifact as indicated by the effect of increasing the medium osmolarity. The process is stimulated by a membrane potential (negative inside) as demonstrated by the effect of the ionophores valinomycin and carbonyl cyanide $\text{m-}\text{chlorophenylhydrazone}$ and anions with different permeabilities. Kinetic data show that tyrosine is accumulated by two systems with different affinities. Tyrosine uptake is inhibited by the presence of phenylalanine and tryptophan.     

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.     

Zoogeographical distribution of Southeast Asian freshwater Calanoida

This paper reviews the systematic status and geographical distribution of 30 odd species of freshwater calanoid copepods in Southeast Asia. Three regions are delineated based on the diversity and abundance of these organisms; Region I being the Southasiatic element, Region II the attenuated belt of copepods and Region III rich in endemic species. The implication of a north-south diminishing of copepod species to inland fisheries is postulated.     

Dissociation of absorptions of calcium and phosphate after successful cadaveric renal transplantation.

Calcium and phosphate absorptions were studied by radiotracer techniques in 30 patients after successful cadaveric renal transplantation, and results were compared with those in a group of normal subjects and in groups of patients with chronic renal failure (CRF). Both calcium and phosphate absorptions were impared in patients with CRF, including those receiving haemodialysis. Abnormalities of calcium absorption, however, seemed to occur earlier in the course of advanced renal failure than abnormalities in phosphate absorption. Calcium absorption improved dramatically after successful renal transplantation, while phosphate absorption remained the same. A dissociation between calcium and phosphate absorptions is not often seen clinically, and the mechanisms for it are unknown. Phosphate malabsorption may be a further contributing factor in the development of persistent hypophosphataemia after transplantation.     

Polypeptide cross-linking in chloroplast membranes

Washed chloroplast membranes from romaine lettuce leaves were treated with the cross-linking reagent dimethyladipimidate (DMA) for various periods of time and subsequently analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Comparative examination of the electrophoretic profiles from control and treated membranes revealed that the light-harvesting chlorophyll-protein complex (LHCPC) was readily cross-linked to yield “dimers” and “oligomers” of higher molecular weight. Two polypeptides, of 25 and 23 kilodaltons, previously identified as two subunits of the LHCPC, were the major cross-linked species; other peptides were also cross-linked, but to a much lesser extent. These results suggest that cross-linking of chloroplast membranes with DMA, under our conditions, occurs primarily among the components of the LHCPC. We also measured the photosystem II activity in control and DMA-treated chloroplasts and found no impairment of this photochemical activity in the cross-linked chloroplasts as compared with controls.