Stability of proteins in the presence of carbohydrates; experiments and modeling using scaled particle theory

How does sucrose stabilize the native state of globular proteins?

“…This conclusion, however, is at odds with the results of a recent study [35,36]. O'Connor and colleagues investigated the effect of sucrose on the thermal stability of RNase A and found that G d (water → 1 M sucrose) = +15 kJ mol −1 at 25 • C. They were able to reproduce this number by means of simple SPT calculations, in the assumption that the E a (sucr) contribution can be neglected [35,36]. To perform SPT calculations at 25 • C, they used the following effective hard sphere diameters: (H 2 O) = 2.76Å, (sucrose) = 8.60Å, (N-state) = 44Å and (D-state) = 56Å (the latter are the effective hydrodynamic diameters determined for RNase A by means of a suitable analysis of capillary electrophoresis measurements at pH 8.4 [35,36]).…”

“…Such a result is in qualitative agreement with those obtained, by means of different theoretical approaches, by Saunders and colleagues [37], and by Schellman [38]. This conclusion, however, is at odds with the results of a recent study [35,36]. O'Connor and colleagues investigated the effect of sucrose on the thermal stability of RNase A and found that G d (water → 1 M sucrose) = +15 kJ mol −1 at 25 • C. They were able to reproduce this number by means of simple SPT calculations, in the assumption that the E a (sucr) contribution can be neglected [35,36].…”

“…O'Connor and colleagues investigated the effect of sucrose on the thermal stability of RNase A and found that G d (water → 1 M sucrose) = +15 kJ mol −1 at 25 • C. They were able to reproduce this number by means of simple SPT calculations, in the assumption that the E a (sucr) contribution can be neglected [35,36]. To perform SPT calculations at 25 • C, they used the following effective hard sphere diameters: (H 2 O) = 2.76Å, (sucrose) = 8.60Å, (N-state) = 44Å and (D-state) = 56Å (the latter are the effective hydrodynamic diameters determined for RNase A by means of a suitable analysis of capillary electrophoresis measurements at pH 8.4 [35,36]). Importantly, O'Connor and colleagues did not use the experimental density of aqueous 1 M sucrose solution, but the density value obtained by imposing that the hard sphere pressure of aqueous 1 M sucrose solution is equal to the hard sphere pressure of neat water, as originally proposed by Berg [39].…”

“…The G d estimates are: 29 kJ mol −1 for 1 M sucrose, 69 kJ mol −1 for 2 M sucrose and 125 kJ mol −1 for 3 M sucrose. These numbers are larger than the "experimental" ones which, assuming a linear dependence of G d upon sucrose molarity, as suggested by measurements on smaller sucrose concentration range [35,36], should be: 15 kJ mol −1 for 1 M sucrose, 30 kJ mol −1 for 2 M sucrose and 45 kJ mol −1 for 3 M sucrose. The large discrepancy between "experimental" and calculated values suggests that the quantity [see Eq.…”

Biocompatible fluorescent silicon nanocrystals for single-molecule tracking and fluorescence imaging

“…3 D. The hydrodynamic diameter of mSiNC was determined to be 4.1 ± 0.2 nm (n = 6; see FCS and determination of the mSiNC size based on the FCS measurements), which was smaller than those of GFP (5.5 ± 0.1 nm; n = 4) and Qdot655 (19.4 ± 0.5 nm; n = 4), consistent with the gel filtration HPLC result. vitamin B12 (hydrodynamic diameter 1.66 nm; Colton et al, 1971) and RNase A (hydrodynamic diameter 4.24 nm; O'Connor et al, 2007;Fig. 3 A).…”