Note on the Small Cloud.-It has been suggested that the Small Magellanic Cloud is also a quasi-barred spiral like the Large Cloud and that its elongation is an indication of its tilt. The variable stars provide no supporting evidence. For 211 cepheid variables in five areas outside the central body of the Small Cloud, we have assembled the mean systematic deviations of the observed median magnitudes from the adopted period-magnitude curve, as shown in the accompanying tabulation. No. of Systematic Area Position Variables Deviation

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Crotoxin, the Brazilian rattlesnake neurotoxin, generally behaves as a homogeneous protein; however, it is a molecular complex of an acidic and a basic protein. These can be separated after alkylation or acylation of the amino groups, or on carboxymethyl cellulose at pH 4, or on DEAE-cellulose in 6 M urea. The two proteins differ greatly in composition, but one or both may exist in the form of closely related variants. Their molecular weights appear to be about 8400 and 13,000.The acidic protein lacks the hemolytic and neurotoxic activity of crotoxin and the basic protein shows only the high, indirect hemolytic activity; a mixture of the two components shows the high neurotoxicity of crotoxin.In 1938, Slotta and Fraenkel-Conrat isolated and crystallized the toxic principle of the venom from Crotalus durissus terriflcus (neotropical rattlesnake) (1). Studies in the ultracentrifuge (2) and in the Tiselius electrophoretic apparatus (3) provided significant evidence for the homogeneity of this protein, crotoxin, and indicated a molecular weight of 30,000 and an isoelectric point of 4.7. This protein carried both the neurotoxic and the indirect, i.e. lecithin-requiring, hemolytic activity of that venom (1). Later, these activities were attributed to separate proteins (4), although no readily reproducible method, nor evidence, for their separation was described (4, 5). The first definitive evidence for the existence of two quite dissimilar proteins in crotoxin came from studies in which the protein was treated with fluorodinitrobenzene (6). Two dinitrophenylated proteins could then be separated, one being soluble and the other insoluble in water. These two proteins differed greatly in their amino acid compositions. No biological activities were detected in these DNP-protein fractions.The purpose of the present study was to purify the two components of crotoxin to a suitable form for biological evaluation. One approach was to replace the dinitrophenyl group by other substituents of amino groups that would favor dissociation of the two proteins, but that could be removed by hydrolysis under mild conditions, e.g., maleyl and methyl maleyl residues (7,8). The other approach was to attempt separation of the two proteins by column chromatography. The previously proposed procedure, DEAE-cellulose near pH 7.0 (4, 5), did not separate proteins of different aminoacid composition (9), but when 6 M urea was added to the solvent (at pH 6.0), or when the native protein was passed over carboxymethyl (CM)-cellulose, an acidic and a basic protein could be isolated. These corresponded in composition to the more soluble and insoluble fractions, respectively, obtained after alkylation or acylation of the amino groups of crotoxin.When the biological activities of these isolated components were tested, the basic protein retained the hemolytic activity, but neither protein showed the toxicity of crotoxin. The combination of the two components, however, was as neurotoxic as was the original complex. MATERIALS AND METHODSFluorodinitro...

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Crotoxin is a potent neurotoxin from the venom of Crotalus durissus terrificus. It is composed of two subunits: a basic phospholipase A2 with low toxicity (component B) and an acidic protein seemingly devoid of intrinsic biological activity (component A). Crotoxin and its isolated phospholipase subunit block the depolarisation caused by cholinergic agonists on the isolated electroplaque from Electrophorus electricus. The other component, which is inactive when applied alone, enhances the pharmacological activity of the phospholipase when the two components are used together. Crotoxin also blocks the increase of z2Na+ efflux caused by carbamylcholine from excitable microsacs prepared from Torpedo marmorata electric organ. Crotoxin therefore acts postsynaptically, but does not interfere with the binding of a-toxin from Nu@ nigricollis to the nicotinic cholinergic receptor site. Instead, like local anesthetics, it stabilizes a desensitized form of the acetylcholine receptor characterized by its high affinity for agonists. The phospholipase component B binds in a nonsaturable manner to receptor-rich membranes. In contrast, component A does not bind to acetylcholine receptor-rich membranes, but completely prevents the non-saturable binding of component B. When the two components are applied together, a saturable binding of the latter is observed with the acetylcholine receptor-rich membranes.Crotoxin, the major component of the brazilian rattle-snake (Crotalus durissus terrificus) venom is a very potent neurotoxin which possesses a phospholipase activity [l]. It is a complex of two distinct protein subunits [2,3] : a strongly basic component (component B, M , 12000) which carries the phospholipase activity and an acidic protein (component A, M , 10000) which has no enzymatic activity and is not toxic by itself. Whereas the isolated subunits are either not or only a little toxic, they recombine into a complex which exhibits the same toxicity as the original material [4,5].The lethal effect of crotoxin has generally been attributed to a presynaptic blockage of the neuromuscular transmission [6]. At this level, it causes a reduction of acetylcholine release by the nerve terminals similar to that observed with /l-bungarotoxin [7], notexin [8,9] and taipoxin [lo]. However, having observed a depression of the response to acetylcholine of the isolated denervated rat diaphragm, VitalBrazil [ l l ] concluded that crotoxin also acts at the postsynaptic level in the mammals. In order to examine a possible postsynaptic action of crotoxin without interference with its presynaptic action, we studied the effect of crotoxin on two postsynapticEnzyme. Phospholipase A2 (EC 3.1.1.4) preparations : the isolated electroplaque from Electrophorus electricus and the acetylcholine receptor-rich membranes from Torpedo marmorata. Crotoxin affects the response of both preparations to cholinergic agonists, and our observations suggest how interactions between the two subunits increase the pharmacological effect of the phospholipase component...

We have previously reported that human cels and tissues contain a 1,N-ethenoadenine (EA) binding protein, which, tuh glycosylase activity, releases both 3-ethyladine (m3A) and eA from DNA treated with methylating agents or the vinyl chloride metabolite chloroacetaldehyde, respectively. We now find that both the partially purified human eA-binding pren and cell-free extracts contaiing the cloned human m3A-DNA glycosylase release all four cyclic etheno adducts-namely eA, 3,N4-ethenoCyte (eC), N2,3-ethen aine (N2,3-eG), and l,N2-ethenoguanine (1,N2-eG). Base

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