let s be a monoid and x a class of s-acts which is closed under coproducts. the object of this article is to find conditions under which all s-acts have x-precovering. we have shown that the existence of torsion-free precovering implies the existence of torsion-free covering. this work is an attempt to further facilitate the study of the conjecture that all s-acts have flat cover.

ALBERT, ~VILLIAM C., AND JOSEPH S. HANDLER. EJect of PGEl, indomethacin, and fo&hloretin phosphate on toad bladder response to ADH Am. J. Physiol, 226(6) : 1382-l 386. 1974.-Exogenous PGEr inhibits the short-circuit current response, as well as the water permeability response of the toad bladder to vasopressin. Since PGEI does not inhibit either response to cyclic AMP, it is thought to act by i...

The effect of Bordetella pertussis adenylate cyclase toxin (ACT) on platelet aggregation was investigated. This cell-invasive adenylate cyclase completely suppressed ADP (10 microM)-induced aggregation of rabbit platelets at 3 micrograms/ml and strongly suppressed thrombin (0. 2 U/ml)-induced aggregation at 10 micrograms/ml. The suppression was accompanied by marked increase in platelet intrace...

Attractive carbocyclic structures are accessed via a highly regio- and enantioselective aminocatalytic γ-addition of cyclic enals to vinyl phosphonates followed by a one-pot intramolecular Horner-Wadsworth-Emmons reaction. It is also demonstrated that nitro olefins can act as electrophiles in a similar reaction concept, providing carbocycles in equally high stereoselectivity.

Histamine, beta-adrenergic amines, and prostaglandins inhibited hemolytic plaque formation by splenic leukocytes from immunized mice. The same agents had previously been shown to prevent both the IgE-mediated release of histamine from human basophils and the immunologically specific cytolytic activity of murine lymphocytes, through stimulation of the production of cyclic AMP in leukocytes. We t...

Cell-to cell communication occurs via a signaling pathway referred to as quorum sensing. There are four main types of these systems according to the chemical nature of signal molecules used by microorganisms to elicit expression of target genes in response to environmental stimuli or need of microbial communities. Type I system acts by using acyl homoserine lactones as signals to trigger the ex...

Signal transduction pathways involving the second messenger cyclic di-GMP [bis-(3'-5')-cyclic di-guanosine monophosphate] occur widely in bacteria where they act to link perception of environmental or intracellular cues and signals to specific alterations in cellular function. Such alterations can contribute to bacterial lifestyle transitions including biofilm formation and virulence. The cellu...

We have found that in rat thymocytes binding of [(125)I]choleragen is followed by cellular accumulation of cyclic 3',5'-AMP which, in turn, is followed by stimulation of amino acid transport. Binding of cholera toxin was complete by 30 min and remained constant for the subsequent 150 min. After stimulation by choleragen, cellular cyclic 3',5'-AMP became maximal by 30 min, after which it decline...

1. The diphosphonates, disodium ethane-1-hydroxy-1,1-diphosphonate (EHDP) and disodium dichloromethylene diphosphonate (Cl2MDP), inhibit bone resorption in animals and in explanted bone in tissue culture. The possibility that these effects might be due to inhibition of skeletal adenylate cyclase has been studied. 2. EHDP and Cl2MDP, added for 30 min to the incubation medium at concentrations kn...