A modified enzymatic-isotopic microassay for serotonin (5HT) using 5HT-N-acetyltransferase partially purified from Drosophila

Serotonin-N-acetyltransferase (EC 2.3.1.5), partially purified from Drosophila melanogaster (DNAT) was substituted for rat liver enzyme (RNAT) in a previously published radioenzymatic assay for serotonin (5HT). The purpose was to determine if this modification would increase the sensitivity and reliability of the original assay. Compared with RNAT, DNAT is 3-4 times more active; it lacks secondary 5HTP decarboxylase activity; and it is more stable. Under conditions of the modified assay, the only radioactive product formed from hypothalamic tissue extracts is 3H-melatonin; which can be measured from as little as 15 pg of serotonin substrate. Thus, substitution of DNAT for RNAT improves the original radioenzymatic assay allowing measurement of endogenous 5HT in hypothalamic nuclei from individual animals.

Chemotherapy combination with cyclophosphamide (CTX) adriamycin (ADM), vincristine (VCR), and VP16-213 in small cell carcinoma of the lung (SCCL)

Twenty-four evaluable patients with small cell carcinoma of the lung were treated with an escalating chemotherapy regimen including Cyclophosphamide, Adriamycin, Vincristine and VP16-213. The initial doses were CTX 800 mg/m2 i.v. day 1; ADR 50 mg/m2 i.v. day 1; VCR 1.4 mg/m2 day 1 weekly; and VP16-213 100 mg/m1 i.v. days 14-18 every 4 weeks, CTX and ADR were escalated by 100 and 10 mg/m2 respectively in each subsequent cycle according to blood count. Hematologic toxicity was minimal and the treatment was well tolerated. Partial responses and complete responses were 9 of 19 and 5 of 19 respectively for patients with limited disease, and 4 of 5 respectively for patients with extensive disease. The overall response rate for the whole group was 79% These results must be considered preliminary.

Expression of a transposable antibiotic resistance element in Saccharomyces

Some eukaryotic genes can be expressed in bacteria but there are few examples of the expression of prokaryotic genes in eukaryotes. Antibiotic G418 is a 2-deoxystreptamine antibiotic that is structurally related to gentamicin but has inhibitory activity against a much wider variety of pro- and eukaryotic organisms. In bacteria, resistance to G418 can be determined by several plasmid-encoded modifiying enzymes and, in view of the broad spectrum of activity of G418, we considered that this antibiotic might be useful as a selective agent for the introduction of these antibiotic resistance genes into a eukaryotic organism such as Saccharomyces cerevisiae. Additional impetus for these experiments came from the knowledge that certain of the G418-resistance determinants in bacteria are carried on transposable elements; a study of the properties of these elements in eukaryotes would be intriguing.

Quantification of antibodies against factor VIII by an immunonephelometric method in a continuous-flow system

A new immunonephelometric method is described for the quantification of antibodies against factor VIII in sera from patients suffering from haemophilia A. We have been able to reduce the reaction time to only 16 minutes, which permits its application to emergency cases. Applying Spearman's test, we have correlated the results obtained by the immunonephelometric and Ruggieri's methods, obtaining r = 0.87, P < 0.01 for n = 11. From the reproducibility studies we obtained SD = 1.16 as maximum dispersion value. Because it is a fully automated method in a continuous-flow system, the possible manual errors are reduced to a minimum; 60 determinations can be carried out in 1 hour.

A new selective agent for eukaryotic cloning vectors

An aminoglycoside antibiotic, G418, has been shown to be an inhibitor of many pro- and eukaryotes at concentrations from 1-300 microgram/ml. A bacterial R-plasmid determinant that phosphorylates and inactivates antibiotic G418 can be introduced into yeast by transformation and expresses resistance to G418. It is suggested that this combination of antibiotic and dominant resistance mechanism may be useful in recombinant DNA studies as a cloning selection in eukaryotes.

Competition between trichodermin and several other sesquiterpene antibiotics for binding to their receptor site(s) on eukaryotic ribosomes

1. Of the five sesquiterpene antibiotics tested and found to inhibit protein synthesis in yeast spheroplasts, trichothecin, trichodermol or trichodermin stabilized polyribosomes whereas, in contrast, verrucarin A or T-2 toxin induced 'run off' of polyribosomes with a corresponding increase in 80S monoribosomes. The effect of fusarenon X on the system could not be determined as the drug failed to enter the cells. 2. [acetyl-14C]Trichodermin bound to yeast polyribosomes with a dissociation constant of 2.10 muM and to yeast 'run off' ribosomes with a dissociation constant of 0.72 muM. 3. Trichothecin, trichodermol, fusarenon X, T-2 toxin and verrucarin A competed with [acetyl-14C]trichodermin for binding to its receptor site on 'run off' ribosomes. The observed competition was quantitatively similar for all drugs tested. In contrast, the five drugs competed to different extents with trichodermin for binding to its receptor site on polyribosomes. Thus trichothecin competed with relative efficiency, whereas verrucarin A competed poorly, and the other drugs occupied intermediate positions between these two extremes. 4. Studies were also carried out with yeast 'run off' ribosomes prepared from both a wild-type strain and a strain resistant to trichodermin. Competition experiments between verrucarin A and [3H]anisomycin indicated that verrucarin A bound to 'run off' ribosomes from the mutant strain less efficiently than to those from the wild-type.

Specific inhibition of translocation by tubulosine in eukaryotic polysomes

The alkaloid tubulosine inhibits the process of peptide chain elongation by eukaryotic polysomes by specifically preventing the elongation-factor-2-dependent step of translocation. Tubulosine does not affect either the elongation-factor-1-dependent binding of aminoacyl-tRNA or peptide bond formation. The site of action of tubulosine appears to be independent from the ribosomal site involved in cycloheximide action, since the alkaloid is active in blocking polymerization and enzymic translocation by polysomes from a yeast mutant resistant to cycloheximide. Furthermore tubulosine does not affect the non-enzymic translocation which takes place in the presence of high potassium ion concentrations, whereas this reaction is strongly inhibited by cyclohemimede. The different steps of translocation are discussed to explain the reactions blocked by tubulosine and cycloheximide.

Inhibitors of protein synthesis in eukarytic cells. Comparative effects of some amaryllidaceae alkaloids

The effects of eighteen compounds obtained from bulbs of the Amaryllidaceae family were tested on (a) animal cell growth, (b) DNA, RNA and protein synthesis by intact cells and (c) protein synthesis in cell-free systems. Dihydrolycorine, haemanthamine, lycorine, narciclasine, pretazettine and pseudolycorine halted HeLa cell growth at 10(-1) mM or lower concentrations. These compounds at their growth inhibitory concentrations block protein synthesis in ascites cells and stabilize HeLa cell polysomes in vivo. Endomyocarditis virus RNA-directed cell-free polypeptide synthesis by an ascites S-30 extract and acetyl-[14C]leucyl-puromycin formation by ascites ribosomes are also inhibited by the six compounds indicated above. It is therefore concluded that they halt protein synthesis in eukaryotic cells by inhibiting the peptide bone formation step.

Quantitative binding of antibiotics to ribosomes from a yeast mutant altered on the peptidyl-transferase center

Quantitative binding studies of [G-3H]anisomycin and [acetyl-14C]trichodermin to sensitive and resistant 80-S ribosomes from yeasts are described in this work. A single mutation, most probably affecting the ribosome peptidyl transferase centre, appears to have pleiotropic effects on the ribosome leading to resistance to trichodermin and anisomycin and to an increased sensitivity to sparsomycin. Resistance to trichodermin is due to a reduced affinity of ribosomes from the mutant for the antibiotic. Ribosomes from the sensitive strain (Y 1661 bind [acetyl-14C]trichodermin with a dissociation constant of 0.99 muM while those from the resistant one (TR1) bind [acetyl-14C]trichodermin with a dissociation constant of 15.4 muM. Similar results are obtained when the binding of [acetyl-14C]trichodermin to Y 166 and TR1 60-S subunits is studied. The mutant TR1 is also resistant to anisomycin. Although trichodermin and anisomycin bind to the ribosome at mutually exclusive sites, the higher affinity binding of [G-3H]anisomycin that is responsible for the inhibition of the peptidyl transferase center is practically identical for Y 166 and TR1 ribosomes. Therefore, the mutation in the ribosome leading to resistance to trichodermin and anisomycin decreases the affinity for trichodermin but not for anisomycin. Trichodermin, trichothecin and fusarenon X inhibit the binding of [G-3H]anisomycin to TR1 ribosomes to a lower extent than to Y 166 ribosomes, suggesting that the resistance of TR1 ribosomes to the effects of trichothecin and fusarenon X is caused by a decrease in the affinity of the ribosomes for these drugs, as was seen with trichodermin. On the other hand, verrucarin A inhibits [G-3H]anisomycin binding to Y 166 and TR1 ribosomes to a similar extent and therefore its affinity for the ribosome does not appear to be affected by the mutation leading to resistance. Trichothecin, trichodermin and fusarenon X appear to have a common binding site on the 60-S ribosomal subunits, which overlaps or is closely linked to the binding sites of anisomycin and verrucarin A.

Simultaneous ribosomal resistance to trichodermin and anisomycin in Saccharomyces cerevisiae mutants

A spontaneous mutant of Saccharomyces cerevisiae resistant to trichodermin has been isolated. It displays cross resistance both in vivo and in vitro to a number of sesquiterpene antibiotics (fusarenon X, trichothecin and verrucarin A) and to the chemically unrelated antibiotic anisomycin. The mutation conferring resistance to anisomycin and trichodermin is expressed in the 60-S subunit of the yeast 80-S ribosome. Mutant ribosomes bind [-14C]trichodermin much less efficiently than wild type ribosomes, suggesting that resistance may be due, at least in part, to this property. However, both types of ribosomes bind [-3H] anisomycin equally. These results suggest that anisomycin and trichodermin have different binding sites on the 60-S subunit of eukaryotic ribosomes, even though previous results have shown that both antibiotics bind to mutually exclusive sites.

Lomofungine as an inhibitor of nucleic acid synthesis in Saccharomyces cerevisiae

1. The antibiotic lomofungin was found to be a potent inhibitor of both DNA and RNA synthesis in Saccharomyces cerevisiae. Under selected growth conditions inhibition of DNA synthesis by the drug preceded inhibition of RNA synthesis. 2. Although in general lomofungin inhibited synthesis of ribosomal RNA and polydisperse RNA more effectively than that of low-molecular-weight RNA, under certain conditions the drug inhibited almost completely synthesis of both 4S and 5S RNA. 3. Inhibition of both RNA and DNA synthesis may be explained if RNA synthesis is required for DNA synthesis in yeast. Alternatively, lomofungin, in addition to interacting with DNA-dependent RNA polymerase, might interfere with a component(s) of the DNA-synthetic apparatus. The drug may thus prove to be of considerable value in studies of DNA synthesis in eukaryotes.

Mode of action of thiolutin, an inhibitor of macromolecular synthesis in Saccharomyces cerevisiae

The sulfur-containing antibiotic thiolutin has been shown to be a potent, reversible inhibitor of the growth of Saccharomyces cerevisiae. Viability was unaffected over the concentration range of 4 to 100 mug/ml. At concentrations as low as 2 mug/ml, the drug inhibited ribonucleic acid (RNA) and protein synthesis in whole cells and spheroplasts. At these low concentrations, protein synthesis continued for a short period of time after RNA synthesis was completely stopped. With higher drug concentrations (greater than 20 mug/ml) protein synthesis was inhibited; concentrations of thiolutin up to 100 mug/ml did not affect translocation or peptide bond formation in cell-free protein-synthesizing systems from yeast. The effect of thiolutin on the activity of partially purified deoxyribonucleic acid-dependent RNA polymerases was examined, and the drug was found to be a potent inhibitor of RNA synthesis in vitro. Inhibition was greatest when the polymerase was preincubated with thiolutin. Several mechanisms are discussed to explain the multiple effects of thiolutin on S. cerevisiae. Since the action of the drug is easily reversed, thiolutin may prove to be of use in studies of various stages of yeast growth.