Concanavalin A: a stopped flow nuclear magnetic resonance study of conformational changes induced by Mn++, Ca++, and alpha-methyl-D-mannoside.

Interaction of calcium and manganese ions with apoconcanavalin A and sugar binding

“…The few reports on the interaction of Mn2+-Con A protein with sugars are somewhat contradictory. Mixtures of Mn2+ or other transition metal ions with apo-Con A are reported to give a limited increase in saccharide activity (Kalb & Levitzki, 1968;Shoham et al, 1973;Sherry et al, 1975;Grimaldi & Sykes, 1975). It has been suggested that this may be caused by incomplete isomerization of the protein to the final conformation (Brewer et al, 1974) or to the fact that most reported work is at pH 5.2 (and higher pH favors sugar binding; Alter et al, 1977).…”

“…The reaction between "aged" Mn(Con A) and Ca2+ ions is particularly interesting. From the change with time of the T)-1 of water protons under the influence of the manganese, after apo-Con A was mixed with Mn2+ and Ca2+, the scheme in eq 8 and 9 was proposed (Grimaldi & Sykes, 1975;Brown et al, 1977). The intermediate was termed the "unlocked" and the final form, identical with native, was referred to as the "locked" protein (Brown et al, 1977).…”

“…The speeding up to the final MUM form when a Ca2+/Mn2+ mixture, rather than either ion alone, is added to apo is undoubtedly related to the observation that Ca2+ increases the binding of the manganese (Sherry & Cottam, 1973;Alter et al, 1977;Brown et al, 1977), alters the ESR of the manganese (Nicolau et al, 1969) and accentuates UV differences (Doyle et al, 1975). In addition there is an attendant overall change in protein conformation (Barber and Carver, 1975;Grimaldi and Sykes, 1975;Richardson and Behnke, 1976;Alter et al, 1977;Brown et al, 1977). The protein remaining after EDTA treatment of the Mn or Ca forms and, which has residual MUM binding, may correspond to a recently reported metastable apo-Con A which binds to MM with an affinity approximately 10% of the double Ca2+ locked form (Koenig et al, 1978).…”

Manganese(II) as magnetic relaxation probe in the study of biomechanisms and of biomacromolecules

“…It was shown that the kinetics of Mn(II) binding was also strongly affected.147 That the addition of Ca(II) to Con A alters the properties of the metal ion at Si was also pointed out by the decrease of Tf1 of solvent water, which was attributed to a decrease in the off rate of an exchanging water ligand of the Mn(II).223-225 Slow time-dependent changes in either the properties of the ion at SI or the activity of the protein upon addition of Ca(II) were also reported. 226,227 The magnetic relaxation dispersion of Tf1 of solvent water at various temperatures140 was interpreted in terms of one rapidly exchanging water on the Mn(II), having the same geometry as in the hexaaquo ion with protons 2.7 A from the Mn(II), but a longer residence lifetime (about 3 X 10-6 s compared with about 7 X 10-8 s). Furthermore, the monosaccharide binding to Mn-Con A had little effect on 7V1, indicating that the sugars do not coordinate directly to the transition metal.…”

Remote double bond migration via rhodium catalysis: a novel enone transposition

“…Treatment of 12 with 0.08 equiv ofRhCl3-3H20 in absolute ethanol at 100 °C for 5 h gave none of the anticipated octalone 13. We isolated the 5,e-unsaturated enone 14 in 90% yield.11 14 Further studies are in progress to examine the potential of this new enone transposition and the ability to migrate remote double bonds to their "more stable position'' with the possibility of bringing about "remote epimerizations''. dt, 42% efe, 19% de).…”