Covalent labeling of the cytoplasmic or luminal domains of the sarcoplasmic reticulum Ca(2+)-ATPase with fluorescent azido dyes

Towards a biocompatible artificial lung: Covalent functionalization of poly(4-methylpent-1-ene) (TPX) with cRGD pentapeptide

Covalent multistep coating of poly(methylpentene), the membrane material in lung ventilators, by using a copper-free "click" approach with a modified cyclic RGD peptide, leads to a highly biocompatible poly(methylpentene) surface. The resulting modified membrane preserves the required excellent gas-flow properties while being densely seeded with lung endothelial cells.

Synthetic haptens as probes of antibody response and immunorecognition

The molecular forces that bind antibody to antigen have long fascinated chemists. The use of synthetic haptens to study immunochemical phenomena can be traced back to the classic work of Karl Lansteiner. His utilization of small-molecule-protein conjugates first demonstrated the shape-selective nature of antibody binding. Later work by Linus Pauling and David Pressman employed multivalent, synthetic ligands to establish the bivalent nature of antibodies and explain the nature of immunoprecipitation. Fluorescent probes such as dansyl, fluorescein, and Ru(bpy)(2+)(3) have been used to study affinity maturation, quantify antibody affinities, and investigate polyclonal antibody heterogeneity. Finally, X-ray crystallography has yielded a molecular picture of how antibodies exercise intermolecular forces (e.g., charge-charge interactions, H-bonding, and Van der Waals) to bind haptens. Studies inspired by Landsteiner's original work continue to play an important role in fields ranging from immunodiagnostics to catalytic antibodies.

Anions that potentiate excitation-contraction coupling may mimic effect of phosphate on Ca2+ release channel

Perchlorate is one of a group of inorganic anions that potentiate excitation-contraction coupling in skeletal muscle. We have compared the effect of perchlorate on the sarcoplasmic reticulum (SR) Ca(2+)-release channel with the effect of inorganic phosphate (Pi), an anion which accumulates in skeletal muscle during exercise. Perchlorate and Pi (10-20 mM) stimulated Ca2+ release from SR vesicles 2- to 3-fold, respectively, and increased ryanodine binding to SR vesicles 1.5-fold. Stimulation of SR Ca(2+)-release channel activity by both perchlorate and Pi was maximal in the presence of micromolar Ca2+ and was associated with an increased affinity of the channel for ryanodine. Other anions known to potentiate muscle contraction (thiocyanate, iodide, and nitrate) also stimulated skeletal muscle SR Ca2+ release and ryanodine binding, as did the Pi analogue vanadate. However, none of the inorganic anions examined altered ryanodine binding to cardiac muscle SR. These results confirm that the SR Ca(2+)-release channel may be a primary site at which perchlorate and other potentiating anions affect skeletal muscle excitation-contraction coupling. In addition, these results demonstrate that the action of these anions on the SR Ca(2+)-release channel resembles that of Pi, a potential endogenous regulator of this channel.

Giant sarcoplasmic reticulum vesicles: a study of membrane morphogenesis

Rabbit sarcoplasmic reticulum vesicles were fused into giant proteoliposomes in a medium of 0.1 M KCl, 10 mM Tris-maleate, pH 7.0, 10 micrograms ml-1 antipain, 10 micrograms ml-1 leupeptin, 25 IU per ml Trasylol, 3 mM NaN3, 3.75% PEG 1500 and 3% DMSO by brief exposure to 37 degrees C, followed by incubation for 4 h at 25 degrees C. Approximately 5-10% of the sarcoplasmic reticulum elements underwent fusion, forming single-walled spherical vesicles of 1-25 microns diameter, in which the polarity of the native membrane was preserved. The Ca(2+)-stimulated ATPase activity remained essentially unchanged after fusion. On exposure to decavanadate in a Ca(2+)-free medium the spherical vesicles assumed a corrugated appearance with the formation of long ridges separated by deep furrows that eventually pinched off longitudinally and separated into numerous long crystalline tubules of uniform (approximately 0.1 microns) diameter. The vanadate-induced transformation of giant vesicles into tubules implies that the geometry of the sarcoplasmic reticulum membrane is determined by the conformation of the Ca(2+)-ATPase.