“Structural modification of an amaranth globulins induced by pH and NaCl”

CASTELLANI, O.F; MARTINEZ, E.N; AÑON, M.C

JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY

AMER CHEMICAL SOC

Año: 1998 vol. 46 p. 4846 - 4853

0021-8561

The influence of pH and NaCl on the structure of globulin-P, the polymerizable amaranth 11S type globulin, was studied by differential scanning calorimetry, gel filtration, and gradient sedimentation. At í ) 0.54, the protein is stable for pH ranging from 5 to 9 but becomes rapidly unfolded as pH decreases below 5. For pH values above 9, globulin-P denatures more gradually than in acidic medium, and it also dissociates into subunits, which are possibly less thermostable. At pH 6.5 or 8.5 and low sodium chloride concentrations (í e 0.01), dialyzed globulin-P destabilizes, yielding species of lower thermal stability. The increase in NaCl concentration up to 0.1 M induces folding of globulin-P toward a more stable structure. Above 0.1 M NaCl, increasing the ionic strength up to í ) 0.5 elevates the denaturation temperature (Td) and denaturation enthalpy (¢H). From í )í ) 0.54, the protein is stable for pH ranging from 5 to 9 but becomes rapidly unfolded as pH decreases below 5. For pH values above 9, globulin-P denatures more gradually than in acidic medium, and it also dissociates into subunits, which are possibly less thermostable. At pH 6.5 or 8.5 and low sodium chloride concentrations (í e 0.01), dialyzed globulin-P destabilizes, yielding species of lower thermal stability. The increase in NaCl concentration up to 0.1 M induces folding of globulin-P toward a more stable structure. Above 0.1 M NaCl, increasing the ionic strength up to í ) 0.5 elevates the denaturation temperature (Td) and denaturation enthalpy (¢H). From í )í e 0.01), dialyzed globulin-P destabilizes, yielding species of lower thermal stability. The increase in NaCl concentration up to 0.1 M induces folding of globulin-P toward a more stable structure. Above 0.1 M NaCl, increasing the ionic strength up to í ) 0.5 elevates the denaturation temperature (Td) and denaturation enthalpy (¢H). From í )í ) 0.5 elevates the denaturation temperature (Td) and denaturation enthalpy (¢H). From í ) 0.1 to 0.5 the content of soluble globulin-P polymers decreases, possibly owing to protein insolubilization. Above 0.5 M, NaCl shows a stabilizing effect reflected by increasing Td, whereasTd, whereas ¢H stays constant; this effect is similar to that found by other authors in some storage proteins.H stays constant; this effect is similar to that found by other authors in some storage proteins.