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 βwell characterized in βplants and
microbes and crystal structures of β-amylases βhave been βobtained from sweet potato, soybean
and Bacillus cereus.
Objective:
Find out correlation between structural and functional stability induced by change 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 correspond
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 βintensity were βdecreased βwhereas βenzymatic
activity remained unchanged, which revealed fenugreek β-amylase is multi-domains enzyme and
catalytic βdomain βis more βstable 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.
Thermal denaturation of Micrococcus lysodeikticus adenosine triphosphatase. Influence of temperature on the circular dichroism, fluroescence and enzymic activity of the protein