Equilibrating metal-oxide cluster ensembles for oxidation reactions using oxygen in water.

Although many enzymes can readily and selectively use oxygen in water-the most familiar and attractive of all oxidants and solvents, respectively-the design of synthetic catalysts for selective water-based oxidation processes utilizing molecular oxygen remains a daunting task. Particularly problematic is the fact that oxidation of substrates by O2 involves radical chemistry, which is intrinsically non-selective and difficult to control. In addition, metallo-organic catalysts are inherently susceptible to degradation by oxygen-based radicals, while their transition-metal-ion active sites often react with water to give insoluble, and thus inactive, oxides or hydroxides. Furthermore, pH control is often required to avoid acid or base degradation of organic substrates or products. Unlike metallo-organic catalysts, polyoxometalate anions are oxidatively stable and are reversible oxidants for use with O2 (refs 8,9,10). Here we show how thermodynamically controlled self-assembly of an equilibrated ensemble of polyoxometalates, with the heteropolytungstate anion [AIVVW11O40]6- as its main component, imparts both stability in water and internal pH-management. Designed to operate at near-neutral pH, this system facilitates a two-step O2-based process for the selective delignification of wood (lignocellulose) fibres. By directly monitoring the central Al atom, we show that equilibration reactions typical of polyoxometalate anions keep the pH of the system near 7 during both process steps.     

A novel cyclin encoded by a bcl1-linked candidate oncogene

We have previously identified a candidate oncogene (PRAD1 or D11S287E) on chromosome 11q13 which is clonally rearranged with the parathyroid hormone locus in a subset of benign parathyroid tumours. We now report that a cloned human placental PRAD1 complementary DNA encodes a protein of 295 amino acids with sequence similarities to the cyclins. Cyclins can form a complex with and activate p34cdc2 protein kinase, thereby regulating progress through the cell cycle. PRAD 1 messenger RNA levels vary dramatically across the cell cycle in HeLa cells. Addition of the PRAD1 protein to interphase clam embryo lysates containing inactive p34cdc2 kinase and lacking endogenous cyclins allows it to be isolated using beads bearing p13suc1, a yeast protein that binds cdc2 and related kinases with high affinity and coprecipitates kinase-associated proteins. Addition of PRAD1 also induces phosphorylation of histone H1, a preferred substrate of cdc2. These data suggest that PRAD1 encodes a novel cyclin whose overexpression may play an important part in the development of various tumours with abnormalities in 11q13.     

Chronic ethanol causes heterologous desensitization of receptors by reducing alpha s messenger RNA

One of the biochemical results of ethanol exposure is a change in the amount of the intracellular second messenger cyclic AMP (cAMP) produced in response to receptor stimulation. In general, acute ethanol exposure increases the amount of cAMP produced on stimulation of receptors coupled to the enzyme adenylyl cyclase via the GTP-binding protein Gs, whereas chronic ethanol exposure has the opposite effect (results for receptors coupled via Gi have been more variable). We previously reported that adaptation to continuous ethanol exposure reduces receptor-stimulated cAMP production by 25-35% in a neuroblastoma cell line (NG108-15), and an even greater reduction of 75% was observed in lymphocytes taken from actively-drinking alcoholics. This reduction in receptor-stimulated cAMP levels was recently confirmed in platelets from alcoholics. None of these studies, however, determined whether more than one receptor coupled to adenylyl cyclase activity was affected in the same cell. Here we report that chronic ethanol exposure causes desensitization of heterologous receptors coupled to Gs as cAMP production mediated by prostaglandin E1 as well as by adenosine is reduced by approximately 30% in NG108-15 cells. We show that, after chronic ethanol exposure, the activity of the alpha subunit of Gs is decreased by 29%, the amount of alpha s protein is decreased by 38.5%, and alpha s messenger RNA is decreased by 30%. Thus, cellular adaptation to ethanol involves a reduction in alpha s mRNA and, as a consequence, reduced cAMP production by heterologous receptors coupled to Gs. Such changes in cAMP production may account for the tolerance and physical dependence on ethanol in alcoholism.     

Genomic instability in Gadd45a-deficient mice.

Gadd45a-null mice generated by gene targeting exhibited several of the phenotypes characteristic of p53-deficient mice, including genomic instability, increased radiation carcinogenesis and a low frequency of exencephaly. Genomic instability was exemplified by aneuploidy, chromosome aberrations, gene amplification and centrosome amplification, and was accompanied by abnormalities in mitosis, cytokinesis and growth control. Unequal segregation of chromosomes due to multiple spindle poles during mitosis occurred in several Gadd45a -/- cell lineages and may contribute to the aneuploidy. Our results indicate that Gadd45a is one component of the p53 pathway that contributes to the maintenance of genomic stability.     

CACP, encoding a secreted proteoglycan, is mutated in camptodactyly-arthropathy-coxa vara-pericarditis syndrome.

Altered growth and function of synoviocytes, the intimal cells which line joint cavities and tendon sheaths, occur in a number of skeletal diseases. Hyperplasia of synoviocytes is found in both rheumatoid arthritis and osteoarthritis, despite differences in the underlying aetiologies of the two disorders. We have studied the autosomal recessive disorder camptodactyly-arthropathy-coxa vara-pericarditis syndrome (CACP; MIM 208250) to identify biological pathways that lead to synoviocyte hyperplasia, the principal pathological feature of this syndrome. Using a positional-candidate approach, we identified mutations in a gene (CACP) encoding a secreted proteoglycan as the cause of CACP. The CACP protein, which has previously been identified as both 'megakaryocyte stimulating factor precursor' and 'superficial zone protein', contains domains that have homology to somatomedin B, heparin-binding proteins, mucins and haemopexins. In addition to expression in joint synovium and cartilage, CACP is expressed in non-skeletal tissues including liver and pericardium. The similarity of CACP sequence to that of other protein families and the expression of CACP in non-skeletal tissues suggest it may have diverse biological activities.