SOME PHARMACOLOGICAL PROPERTIES OF URIDINE NUCLEOTIDES.
(49/594)
Uridine di-, tri- and monophosphates (UDP, UTP and UMP) contracted the goldfish intestine preparation in that order of decreasing potency. Adenosine triphosphate (ATP) sensitized the gut to UTP and UDP but not to UMP. The fluoro-derivatives of UMP and UTP behaved like the unsubstituted nucleotides on the goldfish intestine but the main effect of 6-azaUDP and large amounts of uracil and uridine was to cause a relaxation. Structure-action relationships are discussed on the basis of these findings. UDPglucose and UDPacetylglucosamine each contracted the goldfish intestine but they were 500-times less active than UDP. Other smooth muscle preparations (tortoise jejunum, rat uterus, guinea-pig ileum and the fowl rectal caecum) contracted to UTP and UDP, but large amounts were needed. The cardiovascular effects in rats of UMP, UDP and UTP were complex and mediated mainly through an action on the peripheral blood vessels. In rats treated with phenoxybenzamine, UMP raised the blood pressure while UDP and UTP first lowered then raised the blood pressure. The fall in blood pressure was not abolished by pronethalol or atropine. The uridine phosphates affected the rat isolated heart only under hypoxic conditions. UTP and UDP dilated the blood vessels of the rabbit ear and UTP was six-times more effective than ATP. UTP and UDP were equiactive in increasing the force of beat of the frog isolated heart. UMP also had an effect if large amounts were given. (+info)
THE DEMONSTRATION OF THE SITE OF ACTION OF THE ANTIMETABOLITE DRUG 6-AZAURIDINE BY THE USE OF LEUCOCYTE CULTURES.
(50/594)
The ability of the lymphocyte cultured in vitro to transform and synthesize deoxyribonucleic has been utilized to locate the site of action of a new antimetabolite 6-azauridine which acts by inhibiting nucleic acid synthesis. The exact site can be demonstrated by incorporating into the cultures nucleotides occurring distal and proximal to the presumed site of action of 6-azauridine. (+info)
STUDIES ON THE MODE OF ACTION OF DIPHTHERIA TOXIN. II. EFFECT OF TOXIN ON AMINO ACID INCORPORATION IN CELL-FREE SYSTEMS.
(51/594)
It has been demonstrated that low concentrations of highly purified diphtheria toxin specifically inhibit incorporation of labeled amino acids into polypeptides in extracts from HeLa cells and from rabbit reticulocytes. No inhibition of incorporation occurs in the absence of a specific cofactor. This cofactor has been identified as nicotinamide adenine dinucleotide (NAD). It has been shown that it is one of the steps involving transfer of amino acids from soluble ribonucleic acid to the growing polypeptide chain that is affected by the toxin in the presence of NAD. (+info)
CHROMATOGRAPHIC SEPARATION OF ANNEALED AND ENZYMATICALLY SYNTHESIZED RNA-DNA HYBRIDS.
(52/594)
A procedure is described for the chromatographic detection and isolation of DNA-RNA hybrids on columns of methylated albumin coated on kieselguhr (MAK). Its use is illustrated with both annealed and enzymatically synthesized hybrids. The method has the advantage of a wide range in capacity and resolution and permits actual isolation of the hybrid structure. It is uniquely effective in experiments involving hybridization with small DNA fragments. (+info)
SOME DIFFERENCES IN THE CONJUGATION OF O-AMINOPHENOL AND P-NITROPHENOL BY THE URIDINE DIPHOSPHATE TRANSGLUCURONYLASE OF MOUSE-LIVER HOMOGENATES.
(53/594)
1. Glucuronide synthesis from uridine diphosphate glucuronate and o-aminophenol or p-nitrophenol in the presence of uridine diphosphate transglucuronylase of mouse-liver homogenates has been studied with respect to inhibition by compounds known to be conjugated under the experimental conditions, and also by thiophenol. 2. Raising the o-aminophenol concentration decreased the inhibition of o-aminophenyl glucuronide synthesis by the alternative glucuronyl acceptors phenol, menthol and benzoic acid, but was without effect on that caused by p-nitrophenol and thiophenol. 3. Raising the p-nitrophenol concentration decreased or abolished the inhibition of p-nitrophenyl glucuronide synthesis due to phenol, menthol, benzoic acid, anthranilic acid, o-aminophenol and thiophenol. 4. The o-aminophenol system was much more readily inhibited by all compounds than the p-nitrophenol system. 5. In tris buffer, pH7.4, over 30% activation of the o-aminophenol system was achieved by 2mm-Mg(2+), but 10mm-Mg(2+) was inhibitory. The p-nitrophenol system showed only inhibition from 2mm-Mg(2+) upwards. 6. The results are discussed as suggesting that there are at least two uridine diphosphate transglucuronylases. (+info)
TRANSPORT AND METABOLISM OF THIAMINE IN RAT BRAIN CORTEX IN VITRO.
(54/594)
1. Aerobic incubation at 37 degrees of rat brain-cortex slices in Krebs-Ringer phosphate medium containing glucose and labelled thiamine results in accumulation in the tissue of labelled thiamine and labelled thiamine phosphates. The concentration of the labelled thiamine in the tissue cell water increases with increase of external labelled thiamine concentration in an approximately linear manner, the concentration ratio for labelled thiamine (tissue:medium) exceeding unity with low external thiamine concentrations (e.g. 0.2mum) and diminishing to about unity as the external thiamine concentration is increased to 1mum. The concentration of labelled phosphorylated thiamine in the tissue is at least double that of the labelled thiamine present and its amount increases with increase of external thiamine concentration. Labelled phosphorylated thiamine appears in the medium, its amount being about one-fifteenth of that in the tissue. Phosphorylation of thiamine in the tissue proceeds during incubation for 3hr. and, with an external labelled thiamine concentration of 0.2mum, about 48% conversion of thiamine takes place. 2. In the presence of ouabain (0.1mm), which does not inhibit thiamine phosphorylation in rat brain extract, there is a fall in the uptake of labelled thiamine by brain-cortex slices and the concentration ratio for the labelled thiamine (tissue:medium) falls to below unity. Anaerobiosis, lack of Na(+) or the presence of Amprol (0.01mm) leads to marked inhibition of thiamine phosphorylation, and the concentration ratio for labelled thiamine (tissue:medium) falls to about unity. The facts lead to the conclusion that thiamine is conveyed into the brain cell against a concentration gradient by an energy-assisted process mediated by a membrane carrier. Pyri-thiamine is a marked inhibitor of thiamine phosphorylation in brain extract. 3. Thiamine monophosphate and thiamine diphosphate inhibit thiamine phosphorylation in brain extract. They diminish ;total' thiamine (free and phosphorylated) uptake into brain-cortex slices and inhibit the transport of thiamine into the brain cell, possibly by competition for the carrier. 4. Phosphorylation of labelled thiamine in brain extract is brought about not only by adenosine triphosphate (in the presence of Mg(2+)) but apparently by adenosine diphosphate and uridine triphosphate. (+info)
CHANGES IN THE FREE NUCLEOTIDE PATTERN OF PEA SEEDS IN RELATION TO GERMINATION.
(55/594)
1. Major changes in the free nucleotide and nucleoside pattern of germinating pea seeds are described. 2. During the imbibition phase of germination (0-16hr.) there was a 250% increase in ATP content and a parallel fall in AMP content without detectable change in ADP content. Metabolic implications are discussed. 3. The main nucleoside changes during imbibition were a 93% increase in xanthosine content and a 39% fall in adenosine content. 4. During the last phase of germination, leading to the emergence of the radicle, there is a general fall in free nucleotide content. AMP, ADP and ATP contents decreased 73, 48 and 52% respectively. Acetyl-3'-dephosphocoenzyme A concentration fell by 53%. However, the (NADP(+)+NADPH)/(NAD(+)+NADH) ratio increased, and except for uridine content (52% decrease) the nucleoside pattern changed little. 5. A sixfold increase in the concentration of an unidentified UDP-glycosyl compound occurs at this stage, although the content of UDP-glucose and UDP-galactose remained unchanged. 6. No free purine or pyrimidine bases could be detected at any stage of germination. (+info)
Contribution of de-novo and salvage synthesis to the uracil nucleotide pool in mouse tissues and tumors in vivo.
(56/594)
The relative contribution of de-novo and salvage synthesis to tissue pyrimidine nucleotide pools is an important parameter in the rational design of anti-pyrimidine therapies, but has not been measured in vivo. We have measured the contribution of de-novo synthesis to the total acid-soluble uracil nucleotide pool in mouse tissues by analysis of the incorporation of label after intra-peritoneal infusion of L-[15N]alanine. The contribution of salvage synthesis was measured by the incorporation of radiolabel after intravenous infusion of [14C]uridine. The results show that de-novo synthesis makes the larger contribution to the intestine uracil nucleotide pool, salvage synthesis makes the larger contribution to the kidney pool, and de-novo and salvage synthesis make roughly equal contributions to the liver pool. In tumors studied (L1210, P388, B16, Nettesheim), the contribution of de-novo synthesis was at least five times the contribution of salvage synthesis. The measurements were repeated 24 hours after a 400-mg/kg dose of N-phosphonacetyl-L-aspartic acid. De-novo synthesis was substantially inhibited in all tissues and tumors after this treatment, although significant residual activity was observed in the intestine and L1210 cells. Nettesheim carcinoma was the only tumor or tissue to show a significant increase in salvage synthesis after N-phosphonacetyl-L-aspartic acid treatment. (+info)