Selective killing of Leishmania infected mouse macrophages by 6-methylpurine 2′-deoxyriboside

6-methylpurine 2′-deoxyriboside killed mouse macrophages infected with amastigotes of $\text{Leishmania donovani}$ and $\text{Leishmania mexicana}$, but did not affect the growth of non-parasitized cells. $\text{Leishmania}$ extracts cleaved the non-toxic 6-methylpurine 2′-deoxyriboside to 6-methylpurine, a potent adenine antimetabolite for mammalian cells. By eliminating macrophages latently infected with $\text{Leishmania donovani}$ amastigotes, 6-methylpurine 2′-deoxyriboside could augment the effects of leishmanicidal agents $\text{in vivo}$.     

Solid-phase peptide synthesis of somatostatin using mild base cleavage of N alpha-9-fluorenylmethyloxycarbonylamino acids

Experimental details for the "Fmoc solid phase peptide synthesis" of somatostatin are described. The 9-fluorenylmethyloxycarbonyl group was rapidly and quantitatively cleaved by 55% piperidine in dimethylformamide and monitored (u.v.) manually. For a kinetic study, a centrifugal reactor with a photometric control system and reference cell was used at each stage. The symmetrical anhydride coupling reaction was rapid and either acetic anhydride or fluorescamine termination was incorporated to minimize formation of deletion peptides. Anchor-bond cleavage was effected with trifluoroacetic acid which simultaneously removed all the acid labile tert.-butyl side chain protecting groups. N alpha-9-fluorenylmethyloxycarbonyl peptides may be obtained by omitting the piperidine deprotection step after the last cycle of synthesis. From several syntheses, analytically pure di-S-protected somatostatin 14-peptide was obtained in 55-60% overall yield. The S-protecting groups were removed and the product was purified by gel filtration to give homogeneous dihydrosomatostatin (91%) yield. Oxidation of dihydrosomatostatin with potassium ferricyanide and purification by countercurrent distribution provided analytically pure homogeneous somatostatin.     

Nitrogen control of Salmonella typhimurium: co-regulation of synthesis of glutamine synthetase and amino acid transport systems.

Nitrogen control in Salmonella typhimurium is not limited to glutamine synthetase but affects, in addition, transport systems for histidine, glutamine, lysine-arginine-ornithine, and glutamate-aspartate. Synthesis of both glutamine synthetase and transport proteins is elevated by limitation of nitrogen in the growth medium or as a result of nitrogen (N)-regulatory mutations. Increases in the amounts of these proteins were demonstrated by direct measurements of their activities, by immunological techniques, and by visual inspection of cell fractions after gel electrophoresis. The N-regulatory mutations are closely linked on the chromosome to the structural gene for glutamine synthetase, glnA: we discuss the possibility that they lie in a regulatory gene, glnR, which is distinct from glnA. Increases in amino acid transport in N-regulatory mutant strains were indicated by increased activity in direct transport assays, improved growth on substrates of the transport systems, and increased sensitivity to inhibitory analogs that are trnasported by these systems. Mutations to loss of function of individual transport components (hisJ, hisP, glnH, argT) were introduced into N-regulatory mutant strains to determine the roles of these components in the phenotype and transport behavior of the strains. The structural gene for the periplasmic glutamine-binding protein, glnH, was identified, as was a gene argT that probably encodes the structure of the lysine-arginine-ornithine-binding protein. Genes encoding the structures of the histidine- and glutamine-binding proteins are not linked to glnA or to each other by P22-mediated transduction; thus, nitrogen control is exerted on several unlinked genes.     

Ochratoxin A-induced iron deficiency anemia.

Ochratoxin A at 8 micrograms per g of diet, but not at lower doses, fed to chickens from 1 day to 3 weeks of age resulted in significantly (P less than 0.05) decreased packed blood cell volume and hemoglobin concentration without altering the number of circulating erythrocytes. Serum iron and percentage of transferrin saturation were lowered at 4 and 8 micrograms/g. Therefore, anemia was characteristic of severe ochratoxicosis of young chickens, and the anemia was categorized as a hypochromic-microcytic anemia of the iron deficiency type. These data indicate that ochratoxin A by itself does not cause hemorrhagic anemia syndrome of chickens and that an anemia caused by a nutritional deficiency can be elicited by a mycotoxin.     

Quantitative aspects of hormone-receptor interactions of high affinity: Effect of receptor concentration and measurement of dissociation constants of labeled and unlabeled hormones

It is demonstrated that because of limitations in the magnitude of the specific activity of radiolabeled hormone derivatives, direct binding studies of hormone-receptor interactions of high affinity (10^?9–10^?11 M, depending on whether ³H- or ¹²³I-labeled hormones are used) will be subject to artifactual distortions due to the need to utilize high concentrations of the receptor. If the concentration of the receptor is not ten times lower than the true affinity constant, the apparent dissociation constant obtained from direct concentration binding curves will vary as a linear function of the receptor concentration. In addition, at high receptor concentrations saturability becomes difficult to demonstrate experimentally and the binding data yield apparently non-hyperbolic, sigmoidal curves which can be mistakenly interpreted to depict cooperative interactions. Similar artifacts related to receptor concentration are predicted for measurements of the hormone concentration dependence of biological processes (e.g. activation of adenylate cyclase, transport processes, etc.). Methods for detecting these effects, and correctly measuring affinities for labeled and unlabeled hormones under these conditions, are described. The implications for measuring the binding properties of hormone-receptor interactions are discussed, especially in reference to studies of the comparative analysis of receptor function in altered metabolic states and to studies relating the biological and binding properties of hormones.     

Induction of temporary sterility in female hamsters by an intraperitoneal silastic-PVP-PGF2alpha tube.

In the female hamster, temporary sterility for a period of 10 or 15 days was induced by an intraperitoneal Silastic-PVP-tube containing 3.5 or 1.0 mg of PGF2alpha, respectively. All Silastic-PVP-PGF2alpha tube hearing animals regained fertility and delivered normal litters at various times after the placement of the tube. The release rate of 3-H-PGF2alpha from the Silastic-PVP tube was described and their potential use as a drug delivery system discussed.