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Denaturant induced equilibrium unfolding and conformational transitional studies of germinated fenugreek β-amylase revealed molten globule like state at low pH.

BACKGROUND
β-Amylase (EC 3.2.1.2) is a maltogenic enzyme, which releases β-maltose from the non-reducing end of the substrates. The enzyme plays important roles for the production of vaccine, maltiol and maltose rich syrups. Apart from these applications the enzyme protects cells from abiotic as well as oxidative damage. The enzyme is well characterized in plants and animals and crystal structures of β-amylases have been obtained from sweet potato, soybean and Bacillus cereus.


OBJECTIVE
Find out correlation between structural and functional stability induced by changing in pH, temperature and chaotropes.


METHODS
Activity, intrinsic fluorescence, extrinsic fluorescence, near- and far- ultraviolet circular dichroism spectroscopic measurements were performed.


RESULTS
Peaks about 208 nm and 222 nm obtained by near- ultraviolet circular dichroism corresponds to α-helix whereas peak at 215 nm shows presence of β-sheet. At pH 2.0, absence of tertiary structures, exposed of hydrophobic regions and presence of substantial secondary structures, revealed the existence of molten globule like state. Temperature induced denaturation studies showed that the enzyme was stable up to 75 ºC and the process was found to be irreversible in nature. Chaotropes dependent equilibrium unfolding studies revealed that at low concentration of chaotropes, ellipticity and intrinsic fluorescence intensity were decreased whereas enzymatic activity remained unchanged, which revealed fenugreek β-amylase is multidomains enzyme and catalytic domain is more stable compare to non-catalytic domain. Moreover, the transition was sigmoidal and non-coincidental.


CONCLUSION
Results indicate the probable existence of intermediate states that might perform significant role in physiological process and biotechnological applications.