Thin-layer chromatography of nucleic acid bases, nucleosides, nucleotides and related compounds. 3. Separation of complex mixtures on cellulose layers

Adenosine deaminase of cultured brain cells

Two types of adenosine deaminase (EC 3.5.4.4) were found in cultured cells of central-nervous-system origin. The predominant and more active enzyme was obtained in soluble form from the cytosol of mouse neuroblastoma (N-18), neonatal hamster astrocytes (NN), human oligodendroglioma (HOL) and human astrocytoma (Cox Clone). Particulate adenosine deaminase was probably associated with the plasma membrane. When radioactive adenosine was added to superfusates of monolayer cultures it was rapidly converted into inosine and hypoxanthine. The metabolic conversion required adenosine uptake by the cells, a probable transition through the intracellular ATP pool(s) and a rapid excretion into the superfusate of the catabolic products. We discuss the evidence that points to adenosine and its derivatives as neurohumoral modulators of central-nervous-system function.

Nucleic acid metabolism in yeast VI. Utilisation of exogenous dAMP

It is shown that mutants of Saccharomyces cerevisiae able to efficiently utilise exogenous dTMP can also utilise exogenous dAMP. Under extracellular conditions permissive for dTMP uptake label stemming from offered [8-3H]dAMP is incorporated preferentially into alkali-resistant, high molecular weight material (putative DNA); only about 30% of high molecular weight cell-bound dAMP label was found to be sensitive towards mild alkali hydrolysis. This putative RNA label can be minimised to practically zero when greater than or equal to mM Ade is employed in a dAMP labelling assay. Exogenous dAMP at much greater than 10 microM was found to be cytostatic similarly to much greater than microM dTMP and similarly to inhibit effectively import of exogenous Pi. We conclude from our results that there exists a yeast cytoplasmic membrane permease able to import dAMP. A model of this hypothetical permease system is presented.

Activation of a latent RNAase from yeast by nucleoside triphosphates

A latent RNAase activity stimulated by nucleoside triphosphates has been isolated from a yeast chromatin extract, by filtration on Sepharose 6B and hydroxyapatite chromatography. The RNAase was separated from a thermolabile proteic inhibitor on phosphocellulose. When separated from the inhibitor, the RNAase hydrolyses RNA to 5'-mononucleotides. Its activity is retained in the presence of EDTA, and 50% inhibited by 1 mM ATP or CTP. The RNAase is inhibited by the thermolabile component only in the presence of divalent cations. The activity is recovered upon addition of 0.01 mM ATP to the mixture. The Km for ATP is 10 microM. ATP can be replaced by other ribo- or deoxyribonucleoside triphosphates with varying efficiency but not by ADP, AMP or cAMP. These results suggest multiple interactions between the RNAase, a regulatory component, divalent cations and nucleoside triphosphates.

Nucleoside triphosphate syntheses by chromatin bound enzymes from Morris hepatoma 9121 nuclei

1. Enzymatic syntheses of deoxyribo- and ribonucleoside triphosphates were observed with purified, chromatin bound enzyme C from Morris Hepatoma 9121 nuclei. 2. Intermediate substrates were nucleoside mono- and diphosphates for enzyme C. 3. The three phosphate residues of ATP serving as energy-rich phosphate donor were successively transferred to a nucleoside substrate by enzyme C.

Biological and chemical effects of mustard gas in yeast

Mustard gas induces inactivation and mutation in yeast. Both effects are dose-proportional, indicating single-hit events. Induction of both effects is influenced by the cell's capacity for DNA dark-repair, whereby the probability of reversion is highest in repair-proficient cells. Binding of mustard gas to cells and probably to DNA is independent of DNA-repair systems. The number of inter-strand cross-links, as determined by assaying for renaturability of alkalidenatured DNA, increases in a dose-proportional manner. At 37% survival an excision-deficient strain contains 55 inter-strand cross-links. Chromatographic analysis yields several alkylation products of DNA. Their relative frequencies resemble the values reported for E. coli and bacteriophage T7.

Bacteriophages of Streptococcus pneumoniae. Physicochemical properties of bacteriophage Dp-4 and its transfecting DNA

The properties of Dp-4 phage and its DNA have been studied. The phage has a polyhedral head of 60 nm diameter, a tail 155 nm long and a buoyant density in CsCl of 1.48 g/cm3. Analysis by acrylamide gel electrophoresis indicates the presence of five polypeptides. Dp-4 DNA has a molecular weight of 37 x 10(6), a melting point of 83.5 degrees C (when dissolved in 0.15 M NaCl/0.015 M sodium citrate, pH 7.0) and a G + C content of about 33%. Denaturation of DNA yields two strands of different buoyant density in a neutral CsCl gradient. The interaction of poly(U, G) with the heavy strand strongly enhances its density and allows the preparative separation of both strands. Native Dp-4 DNA has unusual physical properties: abnormally low buoyant densities both in CsCl (1.666 g/cm3) and in Cs2SO4 (1.410 g/cm3) (which do not correspond to the value predictable from the G + C content of the DNA), and a high thermal stability at low ionic strength.

Study of the role of puring phosphoribosyltransferases in the uptake of adenine and guanine by Schizosaccharomyces pombe cells

1. In the yeast Schizosaccharomyces pombe 972h-, the uptake rate of both adenine and guanine is related to variations in the specific activity of the corresponding phosphoribosyltransferases during the growth of the culture. Furthermore, the mutant strains dap 1, devoid of adenine phosphoribosyltransferase activity, and pur 1, devoid of guanine phosphoribosyltransferase activity have a lowered uptake rate of adenine and guanine respectively, along with an increased apparent Km value for these purines in comparison to the wild-type 972h. 2. The uptake rate of the purines is strongly dependent on the pH of the uptake medium in 972h- as well as in the strains dap 1 and pur 1, the optimum being between pH4 and pH5. 3. A new method of extraction of 5-phosphoribosyl-1-pyrophosphate from the yeast has been devised. Important fluctuations of the P-Rib-P2 pool were measured in S. pombe at different stages of growth, the maximum taking place at the start of the exponential phase, whereas no variations in the specific activity of the P-Rib-P2 synthetase could be observed during the growth. The P-Rib-P2 intracellular content in the mutants devoid of purine phosphoribosyltransferases, namely pur 1, dap 1 and pur 1, dap 1, was increased up to 5-fold as compared to the wild-type strain. 4. The effect of intracellular concentrations of P-Rib-P2, a substrate for phosphoribosyltransferases, on the uptake rate of purines has been studied: addition of formycin to the growth medium lowered simultaneously the P-Rib-P2 intracellular content and the uptake of adenine and guanine. 5. Although our results demonstrate the activating effect of phosphoribosyltransferase activities on the uptake of adenine and guanine, they do not support the hypothesis of a 'group translocation' mechanism.

Acid-soluble purine and pyrimidine derivatives in cow's milk produced on normal feed and almost protein-free-feed with urea as the main nitrogen source

In two groups of Ayrshire cows (group I normal feeding with protein, group II got mostly urea as N-source), the TCA-soluble purine and pyrimidine derivatives of the milk were determined quantitatively. The O.D. [U/I] at pH 7-5 and 260 nm was higher in group II than in group I. The difference in N-nutrition of the animals has no influence on the composition of the purine and pyrimidine fractions investigated, especially with regard to orotic acid, uric acid, and CMP. At early stages of lactation the contents of CMP and uric acid were relatively high, but decreased with longer time of lactation. In opposition to this the orotic acid content increased in the same period. These tendencies could be registered in both groups. Besides CMP, uric acid, and orotic acid the minor nucleotides, NAD, AMP, GMP, UMP and others have been determined quantitatively. Their maximum has been found at the beginning of the lactation period and, in general, their contents were higher in group II than in group I.

Incorporation of hypoxanthine into adenine and guanine nucleotides by human platelets

1. Incubation (1-4 h) of normal human washed platelets (5-11-10-8 per ml) with [8-14C] hypoxanthine at a concentration of 10-5 M resulted in a linear incorporation of radioactivity into adenine and guanine nucleotides. 2. Washed platelets from patients with Lesch-Nyhan syndrome, deficient in hypoxanthine: guanine phosphoribosyltransferase, failed to demonstrate any significant incorporation of [8-14C] hypoxanthine but did incorporate [8-14C] adenine like normal platelets under the same incubation condition. 3. These findings are taken to indicate that normal platelets have the enzymes necessary for salvage of hypoxanthine and that hypoxanthine: guanine phosphoribosyltransferase is the obligatory first step in this pathway.

Ribose utilization by Veillonella alcalescens

The utilization of ribose by Veillonella alcalescens has been further investigated. Nonfermentation of ribose is not a result of a phosphorylation lesion since ribose-phosphorylating activity was measured in cell extracts. Resting cells accumulated ribose-5-phosphate and nucleotides when (14)C-ribose was provided; no other sugar phosphates were detectable. Resting cells that were shifted to growth conditions polymerized rather than degraded the accumulated ribose compounds. Cell extracts contained a fructose diphosphate phosphatase. Ribose-5-phosphate, glucose-6-phosphate, and fructose-6-phosphate were not hydrolyzed. It is postulated that the nonfermentation of ribose is not due to any metabolic lesions, but is a consequence of metabolic control at the fructose diphosphate level of glycolysis.