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A number of studies have implicated glycoconjugates in cell recognition events associated with implantation of mammalian blastocysts into the uterus. We have found that p-nitrophenyl-D-xylosides inhibit mouse embryo attachment and outgrowth on monolayers of uterine epithelial cells when cocultured in vitro. Inhibition of attachment and trophoblast formation by alpha- and beta-xylosides was observed in embryos cultured on tissue culture plastic in serum containing medium or on monolayers of epithelial cells. The biochemical basis for this inhibition has been investigated. Consistent with their accepted mode of action, beta- but not alpha-D-xylosides greatly stimulated glycosaminoglycan chain production by uterine epithelial cells and likewise reduced proteoglycan assembly. In contrast, both alpha- and beta-anomers selectively inhibited embryo attachment and outgrowth without stimulating glycosaminoglycan chain production by embryos. The inhibitory effect of the xylosides on embryos was reversible and did not require concentrations that reduced the rate of protein synthesis. Both alpha- and beta-D-xylosides inhibited the synthesis of proteoglycans including heparan sulfate as well as certain other glycoconjugates by embryos. Collectively, these data indicate that proper assembly of glycoconjugates, including proteoglycans, is required for implantation-related processes, although the inhibition of embryo outgrowth by xylosides may be by an as yet uncharacterized mechanism.

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The effectiveness of fluorescence quenching of pyrene-1-sulfonyl azide, a hydrophobic probe used to photo-label acetylcholine receptor (AcChR)-rich electroplax membranes [Sator, V., Gonzalez-Ros, J. M., Calvo-Fernandez, P., & Martinez-Carrion, M. (1979) Biochemistry 18, 1200], is used to study the accessibility of the covalently attached fluorophore to extramembranous quenchers as a function of occupancy of cholinergic receptor binding sites. In these membranes, binding of water-soluble cholinergic ligands to specific sites at the extracellular side affects the fluorophore located in a distant topographical area of the AcChR molecule. When a neurotransmitter analogue (carbamylcholine) is present, the susceptibility of the covalently attached fluorophore to quenching with externally added nitromethane decreases in comparison with that of the same membranes in the absence of carbamylcholine. This neurotransmitter agonist effect is, however, reversible as removal of carbamylcholine by dialysis restores the quenching effectiveness to that of resting nonliganded membranes. The presence of bound alpha-bungarotoxin produces an opposite effect to that of carbamylcholine and induces an increase in susceptibility to quenching agent. These results are interpreted in terms of long-range effects induced by occupancy of cholinergic sites which are detected by covalently bound fluorophore located at regions of the AcChR protein accessible through the lipid matrix of the Torpedo membrane. Such effects are presumably due to molecular rearrangements within the membrane-bound AcChR structure.

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