Decrease In Rate Of Synthesis Research Articles

Biochemistry of mosquito infection: Preliminary studies of biochemical change in Culex pipiens quinquefasciatus following infection with Lagenidium giganteum

The effect of infection of larvae of the mosquito Culex pipiens quinquefasciatus by the fungus Lagenidium giganteum has been studied from a biochemical standpoint. Methods were developed to analyze larval extracts that were essentially free of parasitic material. Biochemical parameters investigated on a per larva basis were protein, and the enzymes o-diphenol oxidase, glutamate transaminase, alkaline phosphatase, trehalase, and chitobiase. The behavior of the total amino acid and sugar pools were also examined. In general it was found that the infected larvae exhibited a significant decrease in rate of synthesis of most of the parameters studied and that the rates eventually fell to zero when compared to healthy control organisms. The progress of mycosis was correlated with visual evidence and it was concluded that the larvae were dying from starvation as a consequence of the utilization of their endogenous reserves by the parasite. Death of the larvae occurred as a general rule, in laboratory conditions, some 48 hr after initiation of infection by the fungus.

Regulation of herpesvirus macromolecular synthesis. I. Cascade regulation of the synthesis of three groups of viral proteins.

Based on evidence that 50% of herpes simplex 1 DNA is transcribed in HEp-2 cells in the absence of protein synthesis we examined the order and rates of synthesis of viral polypeptides in infected cells after reversal of cycloheximide- or puromycin-mediated inhibition of protein synthesis. These experiments showed that viral polypeptides formed three sequentially synthesized, coordinately regulated groups designated alpha, beta, and gamma. Specifically: (i) The alpha group, containing one minor structural and several nonstructural polypeptides, was synthesized at highest rates from 3 to 4 h postinfection in untreated cells and at diminishing rates thereafter. The beta group, also containing minor structural and nonstructural polypeptides, was synthesized at highest rates from 5 to 7 h and at decreasing rates thereafter. The gamma group containing major structural polypeptides was synthesized at increasing rates until at least 12 h postinfection. (ii) The synthesis of alpha polypeptides did not require prior infected cell protein synthesis. In contrast, the synthesis of beta polypeptides required both prior alpha polypeptide synthesis as well as new RNA synthesis, since the addition of actinomycin D immediately after removal of cycloheximide precluded beta polypeptide synthesis. The function supplied by the alpha polypeptides was stable since interruption of protein synthesis after alpha polypeptide synthesis began and before beta polypeptides were made did not prevent the immediate synthesis of beta polypeptides once the drug was withdrawn. The requirement of gamma polypeptide synthesis for prior synthesis of beta polypeptides seemed to be similar to that of beta polypeptides for prior synthesis of the alpha group. (iii) The rates of synthesis of alpha polypeptides were highest immediately after removal of cycloheximide and declined thereafter concomitant with the initiation of beta polypeptide synthesis; this decline in alpha polypeptide synthesis was less rapid in the presence of actinomycin D which prevented the appearance of beta and gamma polypeptides. The decrease in rates of synthesis of beta polypeptides normally occurring after 7 h postinfection was also less rapid in the presence of actinomycin D than in its absence, whereas ongoing synthesis of gamma polypeptides at this time was rapidly reduced by actinomycin D. (iv) Inhibitors of DNA synthesis (cytosine arabinoside or hydroxyurea) did not prevent the synthesis of alpha, beta, or gamma polypeptides, but did reduce the amounts of gamma polypeptides made.

Effects of Clofibrate and of an Estrogen-Progestin Combination on Fasting Biliary Lipids and Cholic Acid Kinetics in Man

The effects of clofibrate and of the combined administration of estrogen plus progestin on the concentration of fasting hepatic bile lipids and on pool sizes and turnover rates of cholic acid were studied. 8 women with normal serum lipids, 1 male with beta-lipoproteinemia, and 1 female with pre-beta-lipoproteinemia were studied after recovery from cholecystecomy. Hepatic bile was collected periodically as long as 4 1/2 months through a closed indwelling cystic duct catheter. Clofibrate lowered serum cholesterol by 15-25% in 3 of the normolipidemic patients. In a patient with hypertriglyceridemia, serum cholesterol fell from 306 to 171 and triglycerides from 520 to 179. Estrogen plus progestin produced a 7% rise in serum cholesterol in 1 patient. Biliary cholesterol increased during clofibrate (7 patients) and hormone (3 patients) administration while bile acid levels were decreased. Cholic acid kinetics in 3 patients showed decreased synthesis rates and pool sizes with both drugs. It is suggested that increased cholesterol saturation of bile during administration of a natural estrogen with progestin to cholecystectomized patients relects an increased propensity to cholesterol formation.

Further studies on catecholamine synthesis in the spontaneously hypertensive rat: Catecholamine synthesis in the central nervous system

Catecholamine levels, turnover rates and in vivo synthesis rates were measured in the brainstems of spontaneously hypertensive rats (SHR) and two normotensive strains, Wistar/NIH and Wistar/Kyoto. All these parameters of catecholamine metabolism were lower in SHR than in the Wistar/NIH but similar to those in the Wistar/Kyoto, the parent strain of SHR. Examination of the three biosynthetic enzymes in the conversion of tyrosine to norepinephrine indicated that all three strains had similar levels of tyrosine hydroxylase and dopamine-β-hydroxylase activity but that the SHR and the Wistar/Kyoto had markedly reduced dopa decarboxylase activity. In vivo synthesis studies using labeled tyrosine and dopa, however, indicated that the decreased synthesis rate in the SHR as compared to Wistar/NIH is the result of decreased amounts of tyrosine entering the catecholamine pool.

Glutathione: VIII. The effects of glutathione disulfide on initiation of protein synthesis

1. 1. Glutathione disulfide (GSSG) additions (1 · 10 −4–2· 10 −4 M or less) to rabbit reticulocyte lysates containing glutathione (GSH) in normal amounts (0.7 · 10 −3–3 · 10 −3 M) have no immediate effect on the rate of protein synthesis at 33°C but cause a rapid decrease in synthesis rate after 6–9 min (the lag period), followed by complete cessation of protein-synthesizing activity. 2. 2. The lag period varies with temperature; the length of the lag period and the time dependence of the decrease in synthesis provide important information for the interpretation of the GSSG effect on protein synthesis. 3. 3. Reduction of GSSG to GSH before or during the lag period prevents inhibition of protein synthesis. Such reduction has no effect on the behavior of the system if carried out after the lag period. 4. 4. Cessation of protein synthesis is accompanied by a conversion of polysomes to monosomes, with little dissociation into subunits. 5. 5. A ribosome-free supernatant is effective in reversing the inhibition of protein synthesis caused by GSSG. Fractionation of the supernatant leads to a protein (precipitated by 40–70 % (NH 4) 2SO 4) which reverses the GSSG inhibition. Further fractionation yields a high molecular weight fraction with inhibition-reversing activity. 6. 6. Factor Q is the name given to the material with inhibition-reversing activity, the inhibition-reversal factor. A scheme for the behavior of Factor Q in protein synthesis is proposed. 7. 7. The effect of the antibiotic, cycloheximide, on initiation of protein synthesis is interpreted in light of the GSSG effect. 8. 8. A small rise in the usual GSSG concentration of a cell is recognized as a potentially important event, one requiring careful scrutiny.