Concanavalin A is known to undergo a first-order conformational transition when metals are added to the demetallized protein at pH 5.6 (Brown, R.D., III, et al. (1977) Biochemistry 16, 3883--3896). The rate constants for this process, which wer have measured using a polarographic technique, are identical when zinc, cobalt, or manganese occupies S1 and calcium occupies S2. The reducible sugar, p-nitrophenyl alpha-D-mannopyranoside, binds only to the locked conformational structure which is formed upon the addition of metals. The affinity of the protein for sugars is dependent upon occupancy of S1 and S2 and quite sensitive to the identity of the metal in S2. The metals may be removed from the locked protein structure and the protein temporarily retains its ability to bind with sugars but with a considerably lower affinity. The locked form of concanavalin A is unstable at a pH near 2 and unfolds to the unlocked structure with a half-life of 25 min resulting in simultaneous loss of metal and sugar binding.

Notes 1459 Meq. of base per gram of sample.geneous solvent is capable of hydrogen bonding with active hydrogen, as is the case with N,N'dimethylformamide, then I could have one of its four hydrogen bridges substituted by a nitrogen bridge and a strongly-acidic proton before the tautomeric equilibrium is affected in the manner described above.

2) The Methobromide of ,3-Dimethylaminoethyl Salicylate.-The bromide I (36.8 g.), salicyloyl chloride (45 g., large excess) and dried benzene (75 8.) are heated on the water-bath until the evolution of gaseous hydrochloric acid ceases. The benzene is decanted, replaced by anhydrous acetone and the mixture boiled for one hour. This procedure is repeated and the solid phase subsequently recrystallized from alcohol as white prisms, m. p. 176', readily soluble in water, difficultly in alcohol; yield, 80%. Anal. Calcd. for ClzHlsOsNBr: Br, 26.3. Found: Br, 26.4.The corresponding iodide, prepared analogously from 11, forms, after recrystallization from alcohol, white needles, m. p. 147-148'; yield, 88%. Anal. Calcd. for CltH1801-NI: N,4.0; L36.2. Found: N,3.9; I, 36.0.

The exchange reaction at polycrystalline lead electrodes in liquid ammonia at --45 ~ ~-1~ has been investigated. At low overpotentials the reaction appears charge transfer controlled. At high overpotentials the reaction is more complex. It is suggested that this is due to the surface being blocked by Pb (NH3) 2 (NO~) 2.Liquid ammonia has considerable attraction for use as a nonaqueous solvent. It has a sizable temperature range in the liquid phase --33.3 ~ to --77.7~ It is interesting for electrochemists since its properties are analogous to those of water. Liquid ammonia dissociates in a similar manner to that of water 2NHs ~-~ NI-I4 + + NH2-

New Compounds 693 centrated at reduced pressure and washed with aqueous sodium bicarbonate and with water, and dried over anhydrous magnesium sulfate. The residue (4.4 g., 82% yield) left by complete removal of solvent was relatively pure ester, m. p. 40-45°. Three recrystallizations from ether-petroleum ether gave 3.0 g. of pure material of constant melting point (41-43°).