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Biotechnology and Applied Biochemistry (2003) 38, (175–181) (Printed in Great Britain)

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Similarities between the thermal inactivation kinetics of Bacillus amyloliquefaciens a-amylase in an aqueous solution of sodium dodecyl sulphate and the kinetics in the solution of anionic-phospholipid vesicles

Atsushi Tanaka*¹ and Eiichi Hoshino†

*Wakayama Research Laboratories, Kao Corporation, 1334 Minato, Wakayama-shi, Wakayama 640-8580, Japan, and †Tokyo Research Laboratories, Kao Corporation, 2-1-3 Bunka, Sumida-ku, Tokyo 131-8501, Japan

Key words: activation parameter, circular dichroism (CD), enthalpy, entropy, surfactant, thermodynamics.

Abbreviations used: BAA, a-amylase from Bacillus amyloliquefaciens; DOPA, dioleoylphosphatidic acid [do not confuse with L-dopa (3,4-dihydroxyphenethylamine)]; c.m.c., critical micellar concentration.

¹To whom correspondence should be addressed (e-mail tanaka.atushi@kao.co.jp).

An anionic surfactant, SDS, is commonly used to model compounds of negatively charged phospholipids. The effect of SDS on the thermal inactivation of BAA (a-amylase from Bacillus amyloliquefaciens) was compared with the effect of negatively charged phospholipid vesicles of DOPA (dioleoylphosphatidic acid) at 40–55 °C. The inactivation kinetics revealed that both SDS below its c.m.c. (critical micellar concentration) and DOPA vesicles accelerated the inactivation and the unfolding of the enzyme structure. Both SDS and DOPA vesicles lowered the activation enthalpy and entropy for the inactivation. The lowered activation parameters might be due to the relatively small energy requirement needed to reach the transition state from the ground state of BAA in the presence of the negatively charged hydrophobic environments. This study suggests an accelerated unfolding of BAA in the presence of SDS to be energetically similar to the accelerated unfolding in the presence of DOPA vesicles that involve a molten-globule-like state.

Received 20 March 2003/3 June 2003; accepted 20 June 2003

Published as Immediate Publication 20 June 2003, DOI 10.1042/BA20030050

© 2003 Portland Press Ltd