Virus metabolic activity

Benzo[a]pyrene has also been shown to affect immune responses to viral infection. Benzo[a]pyrene can reversibly inhibit the induction of viral interferon in 32 different mammalian cell lines but only in the presence of S9 metabolic activation (Hahon and Booth 1988). This inhibition must occur at an early level and not affect viral interferon interactions because the activity of exogenous interferon was unaffected. In addition, influenza virus multiplication was also inhibited by activated benzo[a]pyrene. Benzo[e]pyrene had no effect on interferon induction. The authors suggest that benzo[a]pyrene s inhibition of interferon induction may be an early step in compromising the host s immune function, thereby allowing the induction of carcinogenesis. 

VIRUSES Viruses lack most of the properties that distinguish life from nonlife. For example, viruses cannot carry on metabolic activities on their own. Yet under the appropriate conditions they can wreak havoc on living organisms. Often described as obligate, intracellular parasites, viruses can also be viewed as mobile genetic elements because of their structure, that is, each consists of a piece of nucleic acid... 

Two assays were developed that measure the potency of the FGF-4 transgene carried by Ads FGF-4. In the first case, a one-step growth-promotion assay is conducted on normal, human retinal pigment epithelial cells (ARPE-19). The assay measures metabolic activity (Alamar blue dye metabolism) following infection of ARPE-19 cells with a serial dilution of the virus. The increase in metabohc achvity was measured in relation to a mock-infected control. This increase correlates with FGF-4 produchon determined by an FGF-4 ELISA, increased de-novo DNA synthesis measured by BrdU incorporation, and an increase in cell number. This procedure is therefore an appropriate in-vitro efficacy measure, indicating that the FGF-4 transgene product is biologically active. 

Kocisko et al., 1995 Priola and Chesebro, 1995 Chabry et al, 1998 Cbabry et al, 1999 Horiucbi et al, 1999). That PrP-res can induce PrP-sen to convert to more of tbe abnormal form in a cell-free environment provides compelling evidence that PrP-res can replicate itself in tbe absence of any metabolic activity and demonstrates that a viable virus or bacteria is not needed for tbis process to occur. 

The viruses may be conceived as particles attaching themselves to particular receptors of the succeptible cells. These receptors may be chemical configurations that combine with either viruses or allied substances of similar composition. After due attachment the viruses gain entry into the cell and subsequently multiply. Thus the newly constituted viruses are eventually realised from the cell to paraciticize other cells of the host. In such transformation the metabolic activity of the host cell is modified in some manner. 

Viruses, in general, utilize only the enzyme-system of the host-cell for two purposes, namely first, to synthesize DNA and secondly, to replicate virus, thereby enabling it to perform their usual metabolic activities. They may carry out either the transformation or the replication processes of the cell at the same time. By virtue of the fact that viruses are obligate intracellular parasites, therefore, their replication phenomenon solely depends on the host s cellular processes. 

Parasitism. In this direct interaction a parasite cell or particle attaches Itself to a host cell and makes a partial or total penetration into it, where it then uses the host s biomass or metabolic activities to grow and reproduce itself. Examples are provided by the parasitism of viruses on bacteria and other microorganisms, by the parasitism of the very small bacterium Bdellovibrio on other bacteria, and by the parasitism of bacteria on protozoa (30,74,75). Parasitism is characterized by a variable but always high degree of host specificity. That is, a given parasite is able to Infect only a limited number of hosts, and in some cases, the number may be small Indeed. 

Furman PA, Murakami E, Niu C, Lam AM, Espiritu C, Bansal S, Bao H, Tolstykh T, Steuer HM, Keiiman M et ai (2011) Activity and the metabolic activation pathway of the potent and selective hepatitis C virus pronucleotide inhibitor PSI-353661. Antiviral Res 91 120-132... 

Effect of Ascorbate on Cell Metabolism. We addressed the question of whether ascorbate-induced suppression of RT and p24 production in H9/HTLV-IIIb cells was a virus-specific effect or an indirect effect due to inhibition of cellular metabolism or protein synthesis. The metabolic activity of uninfected H9 cells in the presence and absence of ascorbate was determined by using a quantitative colorimetric assay that utilizes the tetrazolium salt MTT (18). MTT is used to measure the activity of various dehydrogenases in viable cells (18, 19). H9 cells grown in the presence of various concentrations of ascorbate (0-150 /tg/ml) showed an increase in cellular metabolic activity on day 1 (Fig. 4). This correlated with stimulation of cell proliferation by ascorbate. On days 2 and 4, no significant change in metabolic activity was noted between control cultures and those exposed to ascorbate at 75,100, and 150 /xg/ml. 

The salient biochemical fact of phage multiplication is that infection of a rapidly growing cell by a virulent but metabolically inert virus particle produces a cessation of normal synthesis and an almost total diversion of the enzymatic apparatus of the cell to the production of the foreign agent. Actually this statement implies three points that must be demonstrated first, that phage has no metabolic activity, second, that the enzymes of the host cell are used for synthesis of the virus, and third, that only virus is produced after infection. The first of these is most widely accepted for reason of the fact that no virus has ever been shown to possess independent metabolic activity. For animal viruses this conclusion is based mainly on the detailed study of vaccinia and influenza, which Bauer (25) has concluded have no enzymatic activity apart from the questionable instance of mucinase in influenza virus. 

T. Haerde, C.J. Carrera, D.B. Wasson, L.C. Sowers, D.D. Richman, D.A. Carson, Metabolism and anti-human immunodeficienty virus-1 activity of 2-halo-2, 3 -dideoxyadenosine derivatives, J. Biol. Chem. 263 5870 (1988). 

Pauling (65) expresses the foregoing conclusion in other words. He says that a specific type of molecular structure may be the basis of growth, the mechanism of reproduction of viruses and genes, the action of enzymes, the mechanism of the physiological activity of drugs, hormones, and vitamins, and the structure and action of nerve and brain tissue. To these activities of tissues determined by molecular structure, we may add muscular action (55,75), protoplasmic streaming (51,82), and certain metabolic activities of the cell (71) and the body as a whole (75). 

---