Structural stability of soybean (Glycine max) α-amylase: Properties of the unfolding transition studied with fluorescence and cd spectroscopy

Stability and unfolding of mammalian and microbial α-amylases have been intensively investigated. however,there is only limited information available on the structural stability of plant α-amylases,namely of the two isoenzymes from barley amy1 and amy2,of the α-amylase from mung bean (vigna radiata),and of the α-amylase from malted sorghum (sorghum bicolor). we report here the stability of soybean α-amylase (gma),against elevated temperatures and chemical denaturants (gndhcl) by employing circular dichroism and fluorescence spectroscopy. since it is well-known that calcium ions play a crucial role for enzymatic activity and stability of α-amylases,we performed our studies with calcium bound and calcium free gma. the thermal unfolding transition temperature decreased from 72 °c for calcium saturated samples to 57 °c for the case of calcium depleted gma. similarly,the gndhcl transition concentration was lowered from 0.70 m for calcium bound gma to 0.41 m in the absence of calcium. thermal unfolding of gma is irreversible due to aggregation of the unfolded state. gma unfolded in 6 m gndhcl shows high degree of reversibility after diluting the unfolded enzyme in native buffer containing 7 m glycerol. furthermore,the refolded enzyme showed 93% of activity. © 2011 bentham science publishers ltd.