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Experimental evidence has been published from isolated guinea pig muscle in vitro, and from direct ligand binding to receptors from T. californica, indicating that two agonist ions react with the nicotinic receptor by exchanging for one magnesium ion. It is the basis of the ion exchange receptor pair model, in which two acetylcholine ions exchange for one magnesium ion in contact with and between a pair of negatively charged receptor groups about 4 A apart. In the resting state the electrostatic attraction between the negatively charged receptor groups and the Mg2+ ion exerts a binding force. This binding force is opposed by the quantum mechanical repulsions of the electron clouds of the charged groups and ions in contact, together with the mutual repulsion of the pair of receptor oxyanions. When the Mg2+ ion is replaced by two acetylcholine ions the quaternary heads of the latter are positioned so that they form two mutually repelling ACh+ receptor group dipoles. As the Mg2+ ion leaves, its rehydration energy contributes to the sum of the electron cloud repulsions and the ACh+ receptor group dipole repulsions, causing the receptor groups to be forced apart activating the receptor macromolecule. The subsequent decrease in ACh+ concentration results in the reestablishment of the resting state. The coulombic electrostatic energy, the Born repulsion energy, the London attraction energy and the oxyanion ACh+ dipole repulsion energies have been calculated and shown to be consistent with the model. The displacement of the Mg2+ by two ACh+ ions makes several hundred kcals of energy available for receptor group separation and receptor activation.

An attempt has been made to review briefly the present status of the application of solubility measurements to the field of protein chemistry and in particular the quantitative significance of the measurable parameters obtained from the variable solvent solubility test has been evaluated.

Centrifugal filters for SW 25.1 and 50.1 swinging-bucket ultracentrifuge rotors have been tested up to the maximum speeds allowed, 90,000 and 300,000 g , respectively. The filters are 1 and 0.5 in. in diameter and accept standard 25-mm polycarbonate filter membranes. The filter membranes are both cup-shaped to prevent loss of particulates to the support materials of the filters. The filter for the SW 25.1 rotor can take 0.75 ml and that of the 50.1 head 0.5 ml. The fluid retained after centrifuging consists of the fluid on the filter membrane and in its pores and that retained by the material filtered. The calculated volume of the pores of the 0.2-μm filter was 0.46 μl. Total liquid retentions of about 0.8 μl have been achieved with both filters using a particulate concentration of 0.5 mg/ml.

Based on the known curariform action of tris(bipyridyl)iron(II) sulfate and other complex ions, two series of bifunctional ligands designed to hold transition metal ions at approximately the same distance apart as the interquaternary ammonium distance in the potent neuromuscular block agents were synthesized. In the first series two 1,10-phenanthrolines (R1) were joined at the 2 position to form four compounds: R1CO-c-N(CH2CH2)2N-COR1, R1CONH-1,2-C6H10-NHCOR1, R1CONH-1,2-C6H4-NHCOR1, and R1CON(CH3)(CH2)2N(CH3)COR1. In the second series two terpyridines (R1) were joined by different chains to give R2(CH2)2CH=CH(CH2)2R2, R2CH2C(CH3)(OH)(CH2)2C(CH23)(OH)CH2R2, R2CH2C(CH3)(OH)C(CH3)(OH)CH2R2, and R2CH2(OH)-1,4-C6H10-(OH)CH2R2. Three other ligands in which the terpyridines were joined by 5-, 60, and 7-methylene groups were also made. The ligands were converted to nickel(II) complexes and the coordination of each nickel ion was completed by adding terpyridine. These were assayed by the intravenous mouse LD50 method. The most potent ligand, the di-hydroxy compound R2CH2(OH)-1,4-C6H10-(OH)CH2R2 was then converted to the bis(pyridinebipyridine)diosmium-(II) coordinated complex and assayed by the iv mouse LD50 method and by the ED50 isolated guinea-pig diaphragm method. By the iv mouse LD50 method, it was about twice as potent as d-tubocurarine and by the isolated diaphragm method, it was 16 times more potent. The compound has been called dihydroxyosmarine tetrachloride or DHO for short. The term "transarine" ions is proposed for transition metal coordination complexes having curariform action. The position of the transarine ions is discussed in the classification of cholinergic ligands, in structure-action relationships, and in relation to some current ideas on receptor mechanisms.

A filter assay was developed for the specific binding of labeled ligands to the acetylcholine receptor in an unpurified suspension of membrane fragments from Torpedo californica . Binding to the filter membrane and the standard deviation of replicates were studied, and it was possible to reduce relative standard deviation to about 3% by accounting for the variable weight of the particles dispensed, stopping the loss of particles to the filter apparatus, regulating the transmembrane pressure during filtration, controlling the time the filter remains subject to suction after all the liquid has passed through the filter, and correcting for variable counting efficiency. A method for dispensing equal aliquots of suspended particulates is also described.

Based on the known curariform action of tris(bipyridyl)iron(II) sulfate and other complex ions, two series of bifunctional ligands designed to hold transition metal ions at approximately the same distance apart as the interquaternary ammonium distance in the potent neuromuscular block agents were synthesized. In the first series two 1,10-phenanthrolines (R1) were joined at the 2 position to form four compounds: R1CO-c-N(CH2CH2)2N-COR1, R1CONH-1,2-C6H10-NHCOR1, R1CONH-1,2-C6H4-NHCOR1, and R1CON(CH3)(CH2)2N(CH3)COR1. In the second series two terpyridines (R1) were joined by different chains to give R2(CH2)2CH=CH(CH2)2R2, R2CH2C(CH3)(OH)(CH2)2C(CH23)(OH)CH2R2, R2CH2C(CH3)(OH)C(CH3)(OH)CH2R2, and R2CH2(OH)-1,4-C6H10-(OH)CH2R2. Three other ligands in which the terpyridines were joined by 5-, 60, and 7-methylene groups were also made. The ligands were converted to nickel(II) complexes and the coordination of each nickel ion was completed by adding terpyridine. These were assayed by the intravenous mouse LD50 method. The most potent ligand, the di-hydroxy compound R2CH2(OH)-1,4-C6H10-(OH)CH2R2 was then converted to the bis(pyridinebipyridine)diosmium-(II) coordinated complex and assayed by the iv mouse LD50 method and by the ED50 isolated guinea-pig diaphragm method. By the iv mouse LD50 method, it was about twice as potent as d-tubocurarine and by the isolated diaphragm method, it was 16 times more potent. The compound has been called dihydroxyosmarine tetrachloride or DHO for short. The term "transarine" ions is proposed for transition metal coordination complexes having curariform action. The position of the transarine ions is discussed in the classification of cholinergic ligands, in structure-action relationships, and in relation to some current ideas on receptor mechanisms.

SummaryCortisone systemically administered to day-old chicks is a powerful growth inhibitor for the 18-day period of this study. A partial reversal of this growth inhibitory activity of cortisone may be accomplished by the simultaneous administration of beef amniotic fluid.

An accurately machined stainless steel support which enables disposable safety razor blades to be used as microtome knives is described. The blade is attached to the holder with cyanoacrylate cement and is precisely located for maximum rigidity. The surface of the blade is unobstructed by clamps and the device is compatible with regular anti-roll plates.

An improved ultracentrifugal filter for the Beckman SW 50.1 rotor has been tested to 300,000g. The filter is 0.5 in. in diameter, accepts standard 25-mm polycarbonate filter membranes and filters 0.5 ml of solution.