Diadenosine triphosphate (Ap3A) mediates human platelet aggregation by liberation of ADP

Human platelets store considerable amounts of diadenosine 5′, 5′′′-p¹, p³-triphosphate, which is released together with the homologue diadenosine tetraphosphate (Ap₄A) upon thrombin-induced aggregation (Lüthje, J. & Ogilvie, A. (1983) Biochem. Biophys. Res. Commun. 115, 253–260). We now report that, when added to platelet-rich plasma at 10–20 μM, diadenosine triphosphate gradually induces aggregation. The addition of diadenosine tetraphosphate antagonizes this effect by rapidly disaggregating the platelets. When another physiological but structurally unrelated stimulus, i.e. PAF (Platelet activating factor) is introduced into the system, diadenosine triphosphate drastically enhances and prolongs the aggregatory effect of PAF. Again, Ap₄A is antagonistic in this system. The mechanism of Ap₃A-stimulation can be explained by the slow and continuous liberation of ADP from Ap₃A by the action of a hydrolyzing enzyme which is present in human plasma. Our studies suggest that Ap₃A may be physiologically important in providing a relative long-lived stimulus that can modulate platelet aggregation.     

Name that microbe: rapid identification of taxa responsible for individual fragments in fingerprints of microbial community structure

Polymerase chain reaction (PCR)‐based ‘fingerprinting’ methods, such as Terminal restriction fragment length polymorphism, Length Heterogeneity‐Polymerase Chain Reaction (LH‐PCR) and Automated Ribosomal Intergenic Spacer Analysis (ARISA) make possible quantitative studies of microbial community structure and dynamics. Here we outline a strategy for the rapid and cost‐effective isolation of 16S clones corresponding to particular fragment sizes in a fingerprint, based on applying the fingerprinting method to pools of colonies from a clone library. This allows the definitive identification of taxa responsible for the most important bands in the community fingerprint from a full 16S sequence. It offers significant advantages over random selection of clones and removes a significant barrier to the use of these methods.     

Synthesis of hexanucleotide analogues containing diisopropylsilyl internucleotide linkages.

The synthesis of two silyl-linked hexanucleotide analogues is described. Hypochromicity and CD measurements indicate that the thymidine hexanucleotide analogue bears a strong resemblance to its phosphodiester-linked counterpart.     

Steroid-induced proteins secreted by the uterus of the guinea pig.

This study was conducted to identify proteins synthesized and secreted de novo by the guinea pig uterus. Uterine samples were obtained from cycling, late-pregnant as well as ovariectomized and steroid-treated guinea pigs and cultured with either L-[3H]leucine or L-[35S]methionine. Two-dimensional SDS-PAGE of culture medium followed by fluorography was used to determine proteins synthesized and secreted de novo during a 24-h incubation period. Two complexes of estradiol-stimulated proteins (ESP) were detected. Each complex was composed of 5-7 unique proteins with slightly different isoelectric points. The higher molecular-weight complex had a molecular weight of 65,000-60,000 and an isoelectric point range of 5.2-6.1. The lower molecular-weight complex had a molecular weight of 60,000-55,000 and a similar range of isoelectric points. The two complexes of ESP were not observed in medium of explants from animals that received placebos, were late-pregnant, or were treated with progesterone only. Progesterone administered in combination with estradiol enhanced production of both complexes of ESP to similar degrees. Neither complex of ESP was secreted by the explant culture in the presence of tunicamycin, suggesting that the proteins are glycosylated. These findings demonstrate that the uterus of the guinea pig produces two unique complexes of proteins in response to estradiol stimulation, and all results are consistent with the hypothesis that ESP are contained in the carbohydrate-rich secretory granules of endometrial gland cells.     

Affect of spleen and snake venom phosphodiesterases on nucleotides containing nucleosides in the syn conformation.

Dinucleotides containing 6-methyldeoxyuridine and inosine have been prepared and subjected to spleen and snake venom phosphodiesterases. Spleen enzyme degrades all nucleotides tested while snake venom causes very little degradation of nucleotides having 6-methyldeoxyuridine in the 3′-terminal position. The clear implication is that snake venom will not recognize nucleoside units in the syn conformation.     

Inhibition of leucyl-tRNA synthetase in Escherichia coli by the cytostatic 5,8-dioxo-6-amino-7-chloroquinoline.

At concentrations of 1-1.6 mug/ml, 5,8-dioxo-6-amino-7-chloroquinoline causes auxotrophy for leucine in Escherichia coli MRE 600. With increasing concentrations of this quinone additional amino acids are required for growth. The amount of leucine in the pool of free amino acids is not decreased after treatment of E. coli with the quinone. Transfer RNALeu, however, is charged with leucine less than 10% in quinone-treated cells of E. coli, whereas in control cells the degree of aminoacylation is about 85%. From these data we conclude that the quinone causes auxotrophy for leucine by interacting with the charging process of tRNALeu. Quinone was found to inhibit leucyl-tRNA synthetase activity in purified extracts of E. coli with E. coli tRNA as substrate.     

Immunoreactive enzyme protein in medium-chain acyl-CoA dehydrogenase deficiency.

Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency is a common inborn error of mitochondrial fatty acid oxidation. To determine if immunoreactive enzyme protein is present in patients with MCAD deficiency, we studied cultured skin fibroblasts from patients with the 985 point mutation, present in about 85% of cases, and cell lines from patients in which the point mutation is not present or only involves one allele. Immunoblotting studies, using a polyclonal antibody to the purified protein, showed an absence of immunoreactive protein in mitochondrial fractions prepared from fibroblasts from MCAD-deficient patients. To determine whether MCAD protein accumulated in the cytosol because of impaired transport into the mitochondria, we immunoprecipitated MCAD protein from the fibroblast homogenate. MCAD protein was detected in the immunoprecipitates from controls, but not in those from the MCAD-deficient patients. These results suggest that either the MCAD protein is not synthesised or, if produced, it is rapidly degraded.