Velocity of myosin-based actin sliding depends on attachment and detachment kinetics and reaches a maximum when myosin-binding sites on actin saturate

Molecular motors such as kinesin and myosin often work in groups to generate the directed movements and forces critical for many biological processes. Although much is known about how individual motors generate force and movement, surprisingly, little is known about the mechanisms underlying the macroscopic mechanics generated by multiple motors. For example, the observation that a saturating number, N, of myosin heads move an actin filament at a rate that is influenced by actin–myosin attachment and detachment kinetics is accounted for neither experimentally nor theoretically. To better understand the emergent mechanics of actin–myosin mechanochemistry, we use an in vitro motility assay to measure and correlate the N-dependence of actin sliding velocities, actin-activated ATPase activity, force generation against a mechanical load, and the calcium sensitivity of thin filament velocities. Our results show that both velocity and ATPase activity are strain dependent and that velocity becomes maximized with the saturation of myosin-binding sites on actin at a value that is 40% dependent on attachment kinetics and 60% dependent on detachment kinetics. These results support a chemical thermodynamic model for ensemble motor mechanochemistry and imply molecularly explicit mechanisms within this framework, challenging the assumption of independent force generation.     

Time-dependent alterations in the antenna pigment-protein complex by mercury ions in the cyanobacterium Spirulina platensis

We have shown that mercury affects energy transfer in Spirulina platensis. It inhibits energy transfer from phycocyanin to chlorophyll a by specifically bleaching the -84 chromophore of the chromo protein, phycocyanin (PC), in the cyanobacterium. This effect is observed during short-term exposure of cells to Hg²⁺ ions. Upon long-term (12 h) exposure, mercury at low concentrations (1–2.5 m) causes the gradual degradation of the polypeptide (22 kDa) of the PC of phycobilisomes in this cyanobacterium. The effect of mercury on this polypeptide is significant compared with the other phycobiliproteins.     

Effect of polyploidy induction on biomass and ginsenoside accumulations in adventitious roots of ginseng

Adventitious roots ofPanax ginseng C.A. Meyer (a natural tetraploid) were treated with 50 or 100 mg L^-1 colchicine for 12, 24,36, 48, or 60 h to induce polyploid (octoploid) roots. The largest number of octoploid roots was obtained with a 100 mg L^-1 colchicine treatment over 60 h. To verify that ginsenoside was being accumulated in the developing tissues, the tetraploid (control) and octoploid roots were cultured for 40 d in Murashige and Skoog media that lacked NH₄NO₃ but was supplemented with 2 mg L^-1 naphthaleneacetic acid and 50 g L_-1 sucrose. Levels of fresh and dry biomass were greater in the octoploid roots. Although total ginsenoside and Rb-group ginsenoside contents were less in the octoploid roots than in the tetraploids, the former had a higher amount of Rg-group ginsenosides (especially Rg1). These results demonstrate the benefit that polyploid adventitious roots provide in enhancing the production of secondary metabolites in ginseng.     

In vitro propagation of Dendrobium macrostachyum Lindl.--a threatened orchid

In vitro propagation of Dendrobium macrostachyum, a threatened and endemic species was achieved through nodal explants. The nodal explants were cultured on Murashige and Skoog (MS) basal medium and MS medium supplemented with N6-benzyladenine (BA-2.22, 4.44 and 8.88 microM), Kinetin (KN-2.32, 4.65, and 9.29 microM) and Coconut water (CW, 5, 10 and 15%) individually or in combination with 2.69 microM alpha-naphthalene acetic acid (NAA). Axillary shoots were induced directly from nodal explants in medium containing BA, KN or CW. Optimal shoot induction (6 shoots/explant) was attained from nodal explants cultured on medium supplemented with 15% CW. Well developed shoots rooted at an average 5 roots per shoot in half strength MS medium devoid of any growth regulators.     

Resistance of previously infected chimpanzees to successive challenges with a heterologous intraclade B strain of human immunodeficiency virus type 1.

To test whether the protective effects of attenuated simian immunodeficiency virus vaccines in macaques were applicable to the human immunodeficiency virus type 1 (HIV-1)-chimpanzee system, two groups of animals, previously infected with HIV-1(IIIB) or HIV-1(SF2) were each challenged with a heterologous clade B virus, HIV-1(DH12). Following challenge, the parameters measured included virus isolation (from plasma, peripheral blood mononuclear cells, and lymph node tissue); quantitative DNA PCR using primers capable of distinguishing HIV-1(IIIB), HIV-1(SF2), and HIV-1(DH12) from one another; and serologic assays to monitor changes in binding and neutralizing antibodies. In contrast to an HIV-1-naive chimpanzee that rapidly became infected following the inoculation of HIV-1(DH12), the two chimpanzees previously infected with HIV-1(IIIB) resisted repeated and escalating inoculations of HIV-1(DH12), as monitored by virus isolation and PCR. The two animals previously infected with HIV-1(SF2) became infected with HIV-1(DH12) but in contrast to the case with the HIV-1-naive chimpanzee, no cell-free viral RNA was detected in the plasma by the branched DNA procedure and levels of peripheral blood mononuclear cell-associated viral DNA were reduced 35- to 50-fold.     

The consequence of passive administration of an anti-human immunodeficiency virus type 1 neutralizing monoclonal antibody before challenge of chimpanzees with a primary virus isolate.

The anti-gp41 virus neutralizing monoclonal antibody 2F5 was infused into chimpanzees, which were then given an intravenous challenge with a primary human immunodeficiency virus type I (HIV-1) isolate. In two control animals, the infection was established immediately, as evidenced by positive cell-associated DNA PCR and serum RNA PCR tests within 1 week, seroconversion by 4 weeks, and development of lymphadenopathy in this acute phase. Serum RNA PCR tests were negative in one of the two antibody-infused animals until week 8 and in the other antibody-infused animal until week 12; both animals seroconverted at week 14. The peak of measurable virus-specific serum RNA was delayed until week 16 in one antibody-infused animal. Virus-specific RNA in the other animal did not reach levels comparable to those in the other animals through 1 year of follow-up studies. Virus was isolated from the week 16 blood sample from one infused animal. Virus was not isolated from peripheral blood of the second animal but was isolated from lymph node cells taken at week 36. The infection of untreated chimpanzees with this primary isolate appears robust. Use of this isolate should widen the scope of possible experiments in the chimpanzee model. This antibody infusion study indicates that neutralizing antibody, when present at the time of challenge, affects the timing and level of infection and remains influential after it can no longer be detected in the peripheral circulation. It is possible that preexisting, neutralizing antibodies (passively administered or actively elicited) affect the course of acute-phase virus replication in humans. It remains to be established whether these immunologically mediated early effects will influence the course of HIV-1 disease.     

A Preference Based Measure of Complementary Feeding Quality: Application to the Avon Longitudinal Study of Parents and Children

This paper presents the development of the Complementary Feeding Utility Index (CFUI), a composite index aimed to measure adherence to infant feeding guidelines. Through an axiomatic characterization this paper shows the advantages in using the CFUI are the following: it avoids the use of arbitrary cut-offs, and by converting observed diet preferences into utilities, summing the score is meaningful. In addition, as the CFUI is designed to be scored continuously, it allows the transition from intake of beneficial foods (in low quantities) and intake of detrimental foods (in high quantities) to be more subtle. The paper first describes the rationale being the development of the CFUI and then elaborates on the methodology used to develop the CFUI, including the process of selecting the components. The methodology is applied to data collected from the Avon Longitudinal Study of Parents and Children to show the advantages of the CFUI over traditional diet index approaches. Unlike traditional approaches, the distribution of the CFUI does not peak towards mean value but distributes evenly towards the tails of the distribution.     

9-[(Hydroxymethyl)phenyl]adenines: new aryladenine substrates of adenosine deaminase

New phenyl adenine compounds 5-7 were synthesized as analogues of adenosine and studied for their adenosine deaminase (ADA) substrate activity. The 9-[(o-hydroxymethyl)phenyl]methyl]adenine 5 and 9-[(m-hydroxymethyl)phenyl]adenine 7 were deaminated by ADA, and 9-[(o-hydroxyethyl)phenyl]adenine 6 was not deaminated up to 7 days. The ADA substrates 5 and 7 were deaminated quantitatively to their inosine analogues in 10 and 6h, respectively.     

Fulminant Hepatic Failure in Rats Induces Oxidative Stress Differentially in Cerebral Cortex,Cerebellum and Pons Medulla

Hepatic Encephalopathy (HE) is one of the most common complications of acute liver diseases and is known to have profound influence on the brain. Most of the studies, available from the literature are pertaining to whole brain homogenates or mitochondria. Since brain is highly heterogeneous with functions localized in specific areas, the present study was aimed to assess the oxidative stress in different regions of brain-cerebral cortex, cerebellum and pons medulla during acute HE. Acute liver failure was induced in 3-month old adult male Wistar rats by intraperitoneal injection of thioacetamide (300 mg/kg body weight for two days), a well known hepatotoxin. Oxidative stress conditions were assessed by free radical production, lipid peroxidation, nitric oxide levels, GSH/GSSG ratio and antioxidant enzyme machinery in three distinct structures of rat brain-cerebral cortex, cerebellum and pons medulla. Results of the present study indicate a significant increase in malondialdehyde (MDA) levels, reactive oxygen species (ROS), total nitric oxide levels [(NO) estimated by measuring (nitrites + nitrates)] and a decrease in GSH/GSSG ratio in all the regions of brain. There was also a marked decrease in the activity of the antioxidant enzymes-glutathione peroxidase, glutathione reductase and catalase while the super oxide dismutase activity (SOD) increased. However, the present study also revealed that pons medulla and cerebral cortex were more susceptible to oxidative stress than cerebellum. The increased vulnerability to oxidative stress in pons medulla could be due to the increased NO levels and increased activity of SOD and decreased glutathione peroxidase and glutathione reductase activities. In summary, the present study revealed that oxidative stress prevails in different cerebral regions analyzed during thioacetamide-induced acute liver failure with more pronounced effects on pons medulla and cerebral cortex. Murthy Ch.R.K—Deceased while in service.