Stabilizing Effect of Various Polyols on the Native and the Denatured States of Glucoamylase

Different spectral probes were employed to study the stabilizing effect of various polyols, such as, ethylene glycol (EG), glycerol (GLY), glucose (GLC) and trehalose (TRE) on the native (N), the acid-denatured (AD) and the thermal-denatured (TD) states ofAspergillus nigerglucoamylase (GA). Polyols induced both secondary and tertiary structural changes in the AD state of enzyme as reflected from altered circular dichroism (CD), tryptophan (Trp), and 1-anilinonaphthalene-8-sulfonic acid (ANS) fluorescence characteristics. Thermodynamic analysis of the thermal denaturation curve of native GA suggested significant increase in enzyme stability in the presence of GLC, TRE, and GLY (in decreasing order) while EG destabilized it. Furthermore, CD and fluorescence characteristics of the TD state at 71°C in the presence of polyols showed greater effectiveness of both GLC and TRE in inducing native-like secondary and tertiary structures compared to GLY and EG.

Pasteurization Of Antithrombin III: Stabilization By Heparin And Lyotropic Anions

Pasteurization of Antithrombin III (AT III) for 10 hours at 60°C is necessary to reduce the risk of transfusion hepatitis. Addition of appropriate stabilizers can largely prevent the loss of antithrombin activity which otherwise occurs during pasteurization. Studies of the mechanism of denaturation and stabilization have been facilitated by the use of 1,8-anilinonaphthalene sulfonate (ANS) which binds weakly to the inhibitor and whose fluorescence undergoes a sigmoidal response to increasing temperature as the protein unfolds. The extent of the increase in ANS fluorescence correlated roughly with the loss of antithrombin activity and with the extent of protein aggregation as determined by high pressure exclusion chromatography. The midpoint, Td, of the thermal denaturation curve increased by 13 and 19°C in the presence of 0.5 M and 1.0 M sodium citrate respectively. Phosphate, sulfate, and EDTA were also strong stabilizers while the chaotropic anions, iodidé and thiocyanate were potent destabilizers. Heparin, at 10 mg/ml, increased Td by 7°, presumbly through a direct binding mechanism. Reducing agents increased ANS fluorescence by an amount similar to that seen with thermally denatured samples, an effect which was inhibited by heparin but not by citrate. Furthermore, incorporation of 14C-iodoacetamide into AT III during thermal titration was coincident with the increase in ANS fluorescence suggesting that disulfide cleavage is the event which triggers the unfolding of the protein. Samples pasteurized for 10 hours at 60°C in the presence of 0.5 M and 1.0 M citrate retained full antithrombin activity but exhibited evidence of minor alterations in the ability to bind heparin.

Gradual exposure of cystine side-chain residues during urea denaturation of human serum albumin

Showing the accessibility of disulfide groups in the protein molecule, the polarographic catalytic hydrogen current (Brdicka current) was employed for the investigation of the urea denaturation of human serum albumin. The stepwise character of the denaturation curve was accounted for the gradual conformational changes of the protein molecule and related increasing accessibility of cystine side-chain residues.