Growth inhibition of human promonocytic leukaemic U937 cells by interferon gamma is irreversible and not cell cycle phase-specific.

Growth of human promonocytic leukaemic U937 cells was found arrested within 24 h upon exposure to interferon gamma (IFN-gamma). Removal of the interferon did not result in the resumption of growth, as is evident from the absence of doubling of viable cell count and(3)H-thymidine incorporation. 5-Bromo-2'-deoxyuridine-based flow cytometric analysis of the growth-arrested cells, 24 h subsequent to the removal of IFN-gamma, showed absence of DNA synthesis, confirming the irreversible nature of the growth inhibition. Propidium iodide-based flow cytometric analysis of the growth-arrested cells showed a distribution which is typical of a growth inhibition without resulting in the accumulation of cells in any specific phase of the cell cycle. These results indicated that IFN-gamma arrested growth of U937 cells in an irreversible and cell cycle phase-independent manner. These observations were in contrast to our earlier report on the reversible and cell cycle phase-specific growth inhibition of human amniotic (fetal epithelial) WISH cells by the interferon. Copyright 1999 Academic Press.

On a Special Co-cycle Basis of Graphs

In this paper we consider the problems of computing a minimum co-cycle basis and a minimum weakly fundamental co-cycle basis of a directed graph G. A co-cycle in G corresponds to a vertex partition (S,V ∖ S) and a { − 1,0,1} edge incidence vector is associated with each co-cycle. The vector space over ℚ generated by these vectors is the co-cycle space of G. Alternately, the co-cycle space is the orthogonal complement of the cycle space of G. The minimum co-cycle basis problem asks for a set of co-cycles that span the co-cycle space of G and whose sum of weights is minimum. Weakly fundamental co-cycle bases are a special class of co-cycle bases, these form a natural superclass of strictly fundamental co-cycle bases and it is known that computing a minimum weight strictly fundamental co-cycle basis is NP-hard. We show that the co-cycle basis corresponding to the cuts of a Gomory-Hu tree of the underlying undirected graph of G is a minimum co-cycle basis of G and it is also weakly fundamental.

New approximation algorithms for minimum cycle bases of graphs

We consider the problem of computing an approximate minimum cycle basis of an undirected edge-weighted graph G with m edges and n vertices; the extension to directed graphs is also discussed. In this problem, a {0,1} incidence vector is associated with each cycle and the vector space over F-2 generated by these vectors is the cycle space of G. A set of cycles is called a cycle basis of G if it forms a basis for its cycle space. A cycle basis where the sum of the weights of the cycles is minimum is called a minimum cycle basis of G. Cycle bases of low weight are useful in a number of contexts, e.g. the analysis of electrical networks, structural engineering, chemistry, and surface reconstruction. We present two new algorithms to compute an approximate minimum cycle basis. For any integer k >= 1, we give (2k - 1)-approximation algorithms with expected running time 0(kmn(1+2/k) + mn((1+1/k)(omega-1))) and deterministic running time 0(n(3+2/k)), respectively. Here omega is the best exponent of matrix multiplication. It is presently known that omega < 2.376. Both algorithms are o(m(omega)) for dense graphs. This is the first time that any algorithm which computes sparse cycle bases with a guarantee drops below the Theta(m(omega)) bound. We also present a 2-approximation algorithm with O(m(omega) root n log n) expected running time, a linear time 2-approximation algorithm for planar graphs and an O(n(3)) time 2.42-approximation algorithm for the complete Euclidean graph in the plane.

RECONNECT: A NoC for polymorphic ASICs using a low overhead single cycle router

A polymorphic ASIC is a runtime reconfigurable hardware substrate comprising compute and communication elements. It is a ldquofuture proofrdquo custom hardware solution for multiple applications and their derivatives in a domain. Interoperability between application derivatives at runtime is achieved through hardware reconfiguration. In this paper we present the design of a single cycle Network on Chip (NoC) router that is responsible for effecting runtime reconfiguration of the hardware substrate. The router design is optimized to avoid FIFO buffers at the input port and loop back at output crossbar. It provides virtual channels to emulate a non-blocking network and supports a simple X-Y relative addressing scheme to limit the control overhead to 9 bits per packet. The 8times8 honeycomb NoC (RECONNECT) implemented in 130 nm UMC CMOS standard cell library operates at 500 MHz and has a bisection bandwidth of 28.5 GBps. The network is characterized for random, self-similar and application specific traffic patterns that model the execution of multimedia and DSP kernels with varying network loads and virtual channels. Our implementation with 4 virtual channels has an average network latency of 24 clock cycles and throughput of 62.5% of the network capacity for random traffic. For application specific traffic the latency is 6 clock cycles and throughput is 87% of the network capacity.

The key enzyme in galactose metabolism, UDP-galactose-4-epimerase, affects cell-wall integrity and morphology in Candida albicans even in the absence of galactose

The enzyme UDP-galactose-4-epimerase (GAL10) catalyzes a key step in galactose metabolism converting UDP-galactose to UDPglucose which then can get metabolized through glycolysis and TCA cycle thus allowing the cell to use galactose as a carbon and energy source. As in many fungi, a functional homolog of GAL10 exists in Candida albicans. The domainal organization of the homologs from Saccharomyces cerevisiae and C albicans show high degree of homology having both mutarotase and an epimerase domain. The former is responsible for the conversion of beta-D-galactose to alpha-D-galactose and the hitter for epimerization of UDP-galactose to UDP-glucose. Absence of C albicans GAL10 (CaGAL10) affects cell-wall organization, oxidative stress response, biofilm formation and filamentation. Cagal10 mutant cells tend to flocculate extensively as compared to the wild-type cells. The excessive filamentation in this mutant is reflected in its irregular and wrinkled colony morphology. Cagal10 strain is more susceptible to oxidative stress when tested in presence of H2O2. While the S. cerevsiae GAL10 (ScGAL10), essential for survival in the presence of galactose, has not been reported to have defects in the absence of galactose, the C albicans homolog shows these phenotypes during growth in the absence of galactose. Thus a functional CaGal10 is required not only for galactose metabolism but also for normal hyphal morphogenesis, colony morphology, maintenance of cell-wall integrity and for resistance to oxidative stress even in the absence of galactose. (c) 2006 Elsevier Inc. All rights reserved.

Metabolism of Plasmodium berghei. I. Krebs cycle

The free parasites of Plasmodium berghei, obtained from infected cells of rats using an antiserum method, were investigated to study the operation of Krebs cycle. P. berghei was found to respire only with succinate; pyruvate, and other substrates of the Krebs cycle were not oxidized. The presence of a succinate dehydrogenase and a functioning cytochrome oxidase system was demonstrated. Cell-free extracts of free parasites showed the presence of enzymes for the utilization of C4 dicarboxylic acids; other enzymes of the Krebs cycle could not be detected. P. berghei differs from other species of Plasmodium in this respect.

Anthranilic acid oxidase system of Tecomastans—III.: Studies on the conversion of o-aminophenol to catechol

The terminal step in the oxidation of anthranilic acid to catechol by anthranilic acid oxidase system from Tecoma stans, which converts o-aminophenol to catechol has been studied in detail. The reaction catalyses the conversion of one molecule of o-aminophenol to one molecule each of ammonia and catechol. The partially purified enzyme has a pH optimum of 6·2 in citrate-phosphate buffer and a temperature optimum of 45°. The metal ions, Mg2+, Co2+ and Fe3+ were inhibitory to the reaction. Metal chelating agents like 8-hydroxyquinoline, o-phenanthroline, and diethyldithiocarbamate, caused a high degree of inhibition. A sulfhydryl requirement for the reaction was inferred from the inhibition of the reaction by p-chloromercuribenzoate and its reversal with GSH. Atebrin inhibition was reversed by addition of FAD to the reaction mixture.

Conversion of isophenoxazine to catechol in Tecoma stans

Isophenoxazine, formed by the condensation of two molecules of o-aminophenol, is reduced by an enzyme system from Tecoma stans leaves to two molecules of catechol. The reaction proceeds well under anaerobic conditions; a 1–2 mole stoichiometry between the substrate disappeared and the product formed was maintained. The enzyme showed maximum activity at pH 5. The substrate at high concentrations caused a diminution in the activity and the optimum concentration of substrate was at 6 × 10−4 Image . The enzyme preparation was able to convert cinnabarinic acid and diphenylene dioxide 2,3-quinone into the corresponding catechol substances. The diphenylene dioxide 2,3-quinone at the same concentration was three times more susceptible to enzymic cleavage than isophenoxazine. Cinnabarinic acid inhibited the enzymic cleavage of isophenoxazine competitively. None of the known electron donors was found to activate the reaction. Inhibition studies suggested that intact sulfhydryl groups are necessary for enzyme activity. Heavy metal ions like Hg++, Ag+, Co++, Fe++, Ni++, and Fe3++ inhibited the reaction. Metal chelating agents did not have any effect on the enzyme.

The conversion of 3-hydroxyanthranilic acid to cinnabarinic acid by the nuclear fraction of rat liver

Although several authors have implicated 3-hydroxyanthranilic acid (3-OHA) as an intermediate in tryptophaniacin pathway in animals (Kaplan, 1961), alternative pathways of metabolism of this compound have not been fully explored. Madhusudanan Nair obtained an enzyme from spinach leaves which could convert 3-OHA to cinnabarinic acid (private communication). Viollier and Süllmann (1950) reported the conversion of 3-OHA to an unidentified red compound by rat liver homogenates. The present investigation describes the identification of this product as cinnabarinic acid (2-amino-3-H-isophenoxazine-3-one-1,9-dicarboxylic acid). Cinnabarinic acid is known to occur in nature along with cinnabarin is olated from the fungus Polystictus sanguineus (Gripenberg et al., 1957; Gripenberg, 1958).

Enzymatic conversion of anthranilic acid to catechol by chloroplast from the leaves of Tecoma stans

An enzyme system which converts anthranilic acid to catechol was detected in the leaves of Tecoma stans, and its properties studied. The system is present exclusively in the chloroplast fraction of the leaves. The optimum pH of the reaction is 5·2 and maximum activity was obtained with citrate-phosphate buffer. There was good stoichiometry between the amounts of anthranilic acid disappeared and the amounts of catechol and ammonia formed. The enzyme system showed an absolute requirement for oxygen and evidence was obtained for the probable participation of NADPH and FAD in the hydroxylation step. The optimum concentration of anthranilic acid was 10−4 M; at higher concentrations the reaction was inhibited to a considerable extent. Cyanide, pyrophosphate, and EDTA also caused inhibition indicating a requirement for metal ions.

Conversion of an equilenane to the estrane: Synthesis of dl-3-methoxy-17β-carboxy-1,3,5(10)-estratriene

dl-3-Methoxy-11-oxo-17β-carboxy-1,3,5(10),6,8-estrapentaene has been converted to dl-3-methoxy-17β-carboxy-1,3,5(10)-estratriene in fairly good yield.