Association of folate molecules as determined by proton NMR: implications on enzyme binding

The self-association in aqueous solution of folic acid (FA), 7,8-dihydrofolic acid (DHFA) and 5,6,7,8-tetrahydrofolic acid (THFA) has been studied by the use of proton magnetic resonance (1H NMR) spectroscopy. At concentrations below 10 mM, all three folates exist in (monomer)2 in equilibrium dimer equilibria with association constants (Ka) equal to 400, 66 and 14 M-1 for FA, DHFA and THFA respectively. These values decreased markedly to 157, 18 and 3 M-1, for FA, DHFA and THFA respectively, in the presence of 0.8 M KCl. The high extent of dimerization of FA is believed to impede the interaction with the active site of dihydrofolate reductase (DHFR) rendering it a poor substrate. In contrast, the DHFA with a much lower Ka is a better substrate. Conditions that lower the Ka of both FA and DHFA, (i.e., 0.8M KCl) turn them into better substrates. Based on the findings of the present study, it is also predicted that dihydro MTX may be a better inhibitor of DHFR than MTX.     

O-acetyl-salicylic acid promotes colony formation from protoplasts of an elite maize inbred

The salicylic acid derivative acetylsalicylic acid (ASA) was found to promote colony formation from protoplasts isolated from embryogenic suspension cultures of an elite maize inbred line. The drug was most effective at concentrations of 30–100 mg/l, and increases of more than 20-fold in the number of colonies recovered from protoplasts were obtained. The rate of growth of protoplast-derived cell colonies was not affected.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - DMSO dimethylsulfoxide - KM Kao and Michayluk medium (1975) - MES 2[N-morpholino]ethanesulfonic acid - ASA acetylsalicylic acid     

Interleukin inhibition by a parasite proteinase inhibitor, taeniaestatin

A proteinase inhibitor, taeniaestatin, isolated from the larval stage of the cestode Taenia taeniaeformis inhibits endogenous IL 2 generation in murine lymphocytes and IL 1 induced proliferation of murine thymocytes in a dose-dependent manner. However, taeniaestatin does not inhibit exogenous IL 2-induced proliferation of an IL 2-dependent cell line at any dose tested. These data indicate that the lack of IL 2 generation may be due in part to inhibition of a crucial cell-associated proteinase subsequent to cellular activation, or the lack of an effective IL 2 signal for differentiation. Our results are novel findings concerning molecular pathways for parasite inhibition of host immune responses, and suggest that selected proteinase inhibitors may be useful in clinical situations in which IL 1 or IL 2 are elevated.     

X-ray absorption spectroscopy of selenium-containing amino acids

Received: 2 April 1999 / Accepted: 17 September 1999     

Germ Cell Nuclear Factor: An Orphan Receptor in Search of a Function

Germ Cell Nuclear Factor (GCNF) is an orphan member of the nuclearreceptor gene superfamily. Much has been understood about thefunctioning of GCNF which represents a candidate receptor fora novel hormonal signalling pathway. GCNF is not closely relatedto other members of the nuclear receptor superfamily and formsits own branch within the superfamily tree. It has a uniqueexpression pattern that spans both embryonic and adult stagesof development. In the adult, it is expressed in the germ cells:oocytes and spermatogenic cells as well as specific neuronalcells within the brain. In the embryo, GCNF expression is turnedon after gastrulation in all germ layers the ectoderm, mesodermand endoderm. An antero-posterior gradient of GCNF is establishedin the neuroectoderm of the embryo, suggesting a role in regulationof neuronal and germ cell development. Regulation of physiologicalprocesses by a nuclear receptor is achieved through regulationof gene expression. GCNF is the only nuclear receptor to specifcallybind to DR0 hormone response elements to regulate gene expression.In the absense of a ligand, GCNF represses gene expression.GCNF is capable of regulating the expression of the protaminegenes in a response element-dependent manner. At present theligand for GCNF is unknown, but it is hypothesized that GCNFis a receptor for a novel hormonal signalling pathway that effectsits biological response by regulating the expression of a subsetof genes containing DR0 response elements.     

Lipid composition of spinal bone tissue in rabbits of different ages

Studies have been made on the lipid composition of total lipids, triglycerides and their fatty acids, cholesterol and phospholipids in the vertebral column of young and adult rabbits. It was shown that the content of total lipids and triglycerides increases, whereas that of cholesterol and phospholipids decreases with age. The content of total lipids in the vertebral column is 10 times higher as compared to that in the bones of the extremities. Mid-thoracic part of the vertebral column exhibits higher lipid content than other thoracic parts of the column. Lipid content of the vertebral processes is lower than that of the vertebral bodies. These data indicate lipid specificity and heterogeneity of bone tissue of the vertebral column. The main fatty acids of vertebral triglycerides are presented by those with 14-18 carbon atoms (90%), no acids with 22 atoms were found. Higher content of the linoleic acid (19%) and higher total unsaturation of triglycerides were found in the bone tissue of rabbits in comparison with those of man.     

DNA G-quartets in a 1.86 A resolution structure of an Oxytricha nova telomeric protein-DNA complex.

The Oxytricha nova telomere end binding protein (OnTEBP) recognizes, binds and protects the single-stranded 3'-terminal DNA extension found at the ends of macronuclear chromosomes. The structure of this complex shows that the single strand GGGGTTTTGGGG DNA binds in a deep cleft between the two protein subunits of OnTEBP, adopting a non-helical and irregular conformation. In extending the resolution limit of this structure to 1.86 A, we were surprised to find a G-quartet linked dimer of the GGGGTTTTGGGG DNA also packing within the crystal lattice and interacting with the telomere end binding protein. The G-quartet DNA exhibits the same structure and topology as previously observed in solution by NMR with diagonally crossing d(TTTT) loops at either end of the four-stranded helix. Additionally, the crystal structure reveals clearly visible Na(+), and specific patterns of bound water molecules in the four non-equivalent grooves. Although the G-quartet:protein contact surfaces are modest and might simply represent crystal packing interactions, it is interesting to speculate that the two types of telomeric DNA-protein interactions observed here might both be important in telomere biology.     

Multicenter evaluation of the performance and clinical utility in longitudinal monitoring of the Bayer Immuno 1 complexed PSA assay.

We conducted a multicenter evaluation of the analytical and clinical performance of the automated Bayer Immuno 1 complexed PSA (cPSA) assay, and compared assay performance to the Bayer Immuno 1 PSA assay. We sought to determine whether measurements of cPSA could be of clinical utility in the management of patients with prostate cancer. Results of the 10-day imprecision across three evaluation sites produced total CV < 2.50% and an analytical sensitivity of 0.02 microgram/L. There was an increased trend in clinical sensitivity for prostate cancer with increasing stage of disease (71-86%). Clinical specificity for patients with benign urogenital disease was 74.8%, and for other nonprostate diseases ranged from 91.1-100%. Retrospective serial monitoring of 155 patients with prostate cancer demonstrated concordance of cPSA measurements to clinical status for 97% of the patients analyzed. Results from the clinical studies using the Bayer Immuno 1 cPSA assay were comparable to results obtained with the Bayer Immuno 1 PSA assay. The Bayer Immuno 1 cPSA assay demonstrates analytical performance and clinical effectiveness in the management of prostate cancer patients during the course of disease and therapy.     

Delayed nucleoid segregation in Escherichia coli

To study the role of cell division in the process of nucleoid segregation, we measured the DNA content of individual nucleoids in isogenic Escherichia coli cell division mutants by image cytometry. In pbpB(Ts) and ftsZ strains growing as filaments at 42 degrees C, nucleoids contained, on average, more than two chromosome equivalents compared with 1.6 in wild-type cells. Because similar results were obtained with a pbpB recA strain, the increased DNA content cannot be ascribed to the occurrence of chromosome dimers. From the determination of the amount of DNA per cell and per individual nucleoid after rifampicin inhibition, we estimated the C and D periods (duration of a round of replication and time between termination and cell division respectively), as well as the D' period (time between termination and nucleoid separation). Compared with the parent strain and in contrast to ftsQ, ftsA and ftsZ mutants, pbpB(Ts) cells growing at the permissive temperature (28 degrees C) showed a long D' period (42 min versus 18 min in the parent) indicative of an extended segregation time. The results indicate that a defective cell division protein such as PbpB not only affects the division process but also plays a role in the last stage of DNA segregation. We propose that PbpB is involved in the assembly of the divisome and that this structure enhances nucleoid segregation.