The relative effectiveness of 6-thioguanine and 8-azaguanine in selecting resistant mutants from two V79 Chinese hamster cells in vitro

The frequency of surviving colonies in two V79 cell lines exposed to either 6-thioguanine or 8-azaguanine was dependent on initial plating density. Different degrees of metabolic-co-operation were found to occur in the two cell lines and the loss of both spontaneous and added mutants occurred at a lower cell density when 6TG was used for selection than when 8 AZ was used in both cell lines. Both analogues were degraded on incubation in medium plus serum in the absence of added cells. Variation in serum batch had little effect on the rate of degradation or on the frequency of colonies recovered after treatment of V79 cell lines with 8AZ. The reasons for preferring 8AZ to 6TG as a selective agent are discussed.     

Depression of legume growth by liming

Summary Early growth or nodulation of certain species was depressed when a Hawaiian Oxisol was limed at rates above 6 tons/ha (pH 6). In 8 legumes, the depression later gave way to positive response. This was evident in plant weights of Desmodium intortum and Glycine wightii var. Cooper, and in pod weights of Phaseolus vulgaris. A transient depression was observed visually in Desmodium canum, Dolichos axillaris, Glycine wightii var. Tinaroo, and Trifolium subterraneum. In Stylosanthes guyanensis and S. fruticosa, the depression persisted throughout the experiment (6 months). Growth was not depressed in Arachis hypogea, Coronilla varia, Glycine max, Leucaena leucocephala, Medicago sativa, Trifolium repens, or Vigna sinensis. Journal Series No. 1953 of the Hawaii Agr. Exp. Station Journal Series No. 1953 of the Hawaii Agr. Exp. Station     

The evolutionary significance of phase-separated microsystems

The source, preparation, and properties of phase-separated systems such as lipid layers, coacervate droplets, sulphobes, and proteinoid microspheres are reviewed. These microsystems are of interest as partial models for the cell and as partial or total models for the protocell. Conceptual benefits from study of such models are: clues to experiments on origins, insights into principles of action and, in some instances, presumable models of the origin of the protocell. The benefits to evolution of organized chemical units are many, and can in part be analyzed. Ease of formation suggests that such units would have arisen early in primordial organic evolution. Integration of these various concepts and the results of consequent experiments have contributed to the developing theory of the origins of primordial and of contemporary life.Invited paper. Presented at the International Seminar Origin of Life, 2–7 August 1974, Moscow, U.S.S.R.     

Lecithin agar for detection of microbial phospholipases.

Lecithin agar was developed on which phospholipase C produced turbid zones and phospholipase A produced clear zones. Reactions on lecithin agar agreed 74% of the time with reactions in egg yolk broth. On lecithin agar, interpretation was easier, phospholipase A was detectable, and opaque zones were visible 1 or 2 days earlier than on egg yolk agar. All constituents of the medium can be autoclaved.     

Hypoxanthine-guanine phosphoribosyltransferase: Mosaicism in the peripheral erythrocytes of a heterozygote for a normal and a mutant enzyme

A mutant form of erythrocyte hypoxanthine-guanine phosphoribosyltransferase with an abnormal isoenzyme pattern was found in a patient with a partial enzyme deficiency and X-linked gout. This abnormal pattern was a marker for the mutant enzyme in hemolysate from the heterozygote for the enzyme deficiency.These studies were generously supported by the Medical Research Council of Canada (MRC # MA4758) and the Canadian Arthritis and Rheumatism Society.     

Purine catabolism in man: inhibition of 5'-phosphomonesterase activities from placental microsomes.

The 5'-phosphomonoesterase activity of 5'-nucleotidase (EC 3.1.3.5) and alkaline phosphatase (EC 3.1.3.5) participates in the catabolism of purine ribonucleotides to uric acid in humans. Initial velocity studies of 5'-nucleotidase suggest a sequential mechanism of interaction between AMP nad MgCl2, with a Km of 14 and 3 muM, respectively. With product inhibition studies the apparent Ki's for adenosine, inosine, cytidine, and inorganic phosphate were 0.4, 3.0, 5.0, and 42 mM, respectively. A large number of nucleoside mono-, di-, and tri-phosphate compounds were inhibitors of the enzyme. Allopurinol ribonucleotide, ADP, or ATP were competitive inhititors when AMP was the substrate, with a Ki slope of 120 muM. The phosphomonoesterase activity of human placental microsomal alkaline phosphatase had a pH optimum of 10.0 and had only 18% of maximum activity at pH 7.4. Substrates and inhibitors included almost any phosphorylated compound. The Km for AMP was 0.4 mM and the apparent Ki for Pi was 0.6 mM. Activity was increased only 19% by 5 mM MgCl2. These observations suggest that 5'-nucleotidase and alkaline phosphatase may be inhibited by ATP and Pi, respectively, under normal intracellular conditions, and that AMP may be preferentially hydrolyzed by 5'-nucleotidase.     

Transplantation of tumour with a kidney graft.

A cerebral glioma discovered by angiography and brain biopsy in a kidney donor was subsequently suspected of being a secondary tumour. By this time a biopsy of one of the transplanted kidneys had shown a clump of malignant cells in a glomerulus. Because of the psychological state of this recipient the transplant was not removed, but the recipient of the second kidney was immediately told of the danger of tumour cell transfer, and underwent nephrectomy. The patient remained well on haemodialysis; multiple sectioning of the kidney showed no signs of tumour. The transplant in the first recipient functioned well until his death, six months after operation. At necropsy undifferentiated tumour was found in the pleura, liver, pelvic peritoneum, and transplanted kidney. All cadaver donors should undergo full laparotomy after removal of the kidneys, particularly those with a high risk of cancer, and a full necropsy should also be performed shortly afterwards to exclude tumour and other unsuspected diseases. Then it is not too late to remove a transplanted kidney should a tumour be found.     

Genetic Heterozygosity in Unreplicated Bacteriophage λ Recombinants

Bacteriophage crosses using density-labeled parents have been carried out under conditions restricting DNA synthesis. The parental material and genetic contributions to progeny manifesting recombination within a genetic interval sufficiently short to exhibit high negative interference have been examined. The unreplicated products of recombination isolated as phage particles appear to contain long continuous heteroduplex regions which are heterozygous for the closely linked markers. Recombination between closely linked markers seems to be the consequence of the removal of base-pair mismatches that are present within the heteroduplex regions. This localized reduction of heterozygosity within the heteroduplex regions that join the parental components of recombinant DNA molecules can account for high negative interference.     

Intercellular communication in the rat anterior pituitary gland: an in vivo and in vitro study

The concept of "stimulus-secretion coupling" suggested by Douglas and co-workers to explain the events related to monamine discharge by the adrenal medulla (5, 7) may be applied to other endocrine tissues, such as adrenal cortex (36), pancreatic islets (4), and magnocellular hypothalamic neurons (6), which exhibit a similar ion-dependent process of hormone elaboration. In addition, they share another feature, that of joining neighbor cells via membrane junctions (12, 26, and Fletcher, unpublished observation). Given this, and the reports that hormone secretion by the pars distalis also involves a secretagogue-induced decrease in membrane bioelectric potential accompanied by a rise in cellular [Ca++] (27, 34, 41), it was appropriate to test the possibility that cells of the anterior pituitary gland are united by junctions.     

Marker discrimination in deoxyribonucleic acid-mediated transformation of various Pneumococcus strains.

The function responsible for discrimination among markers (point mutations) in Pneumococcus (hex) was traced back to the early strains used to demonstrate the chemical basis of transformation in the early 1940s. Those currently used laboratory strains failing to manifest this function arose from a single subline of the original strain. The function was also evident in other independently isolated strains including a number of different serological types. The hex function was not evident in transformation between heterologous pneumococcal strains probably as a result of the sensitivity of the function to saturation in the presence of deoxyribonucleic acid from closely related but nonisogenic strains.