Purification and characterization of the bile salt hydrolase (BSH) from and regulation of BSH activity in Lactobacillus sp. strain 100-100
Lundeen, Scott Graham
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https://hdl.handle.net/2142/21419
Description
Title
Purification and characterization of the bile salt hydrolase (BSH) from and regulation of BSH activity in Lactobacillus sp. strain 100-100
Author(s)
Lundeen, Scott Graham
Issue Date
1991
Doctoral Committee Chair(s)
Miller, Charles G.
Department of Study
Microbiology
Discipline
Microbiology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Microbiology
Language
eng
Abstract
My thesis research has focused on the bile salt hydrolases (BSH) in gastric lactobacilli. This enzyme catalyzes the deconjugation of bile salts. Several strains of lactobacilli were screened for their capacity to produce this enzyme. Lactobacillus sp. strain 100-100 was found to have high levels of BSH activity and therefore, used as the source of the enzyme.
Initially, two forms of the BSH were purified from strain 100-100. These two isozymes (BSH A and BSH B) differed only in their native molecular weights and subunit composition; catalytically they were similar. Four enzymes with bile salt hydrolase activity, BSH A, B, C, and D, were ultimately purified from strain 100-100. These four proteins consisted of two structurally distinct subunits, $\alpha$ and $\beta.$ They associated with each other forming trimers. The isozymes are the array of possible combinations of the two subunits $\alpha\sb3,$ $\alpha\sb2\beta\sb1,$ $\alpha\sb1\beta\sb2,$ $\beta\sb3$ (BSH A, B, C, and D).
Growth phase and conjugated bile salts regulate BSH activity. It increased 70-fold in cultures of strain 100-100 when they reached stationary phase; conjugated bile salts added to stationary phase cultures of the strain simulated hydrolase activity in whole cells as much as six-fold. However, the enzymatic activity in lysates prepared from cells incubated with such salts was not higher. This led to the discovery of an inducible extracellular compound with the capacity to stimulate BSH activity in whole cells.
This substance was a lipid or had a lipid moiety, appeared to be a large aggregate, was resistant to heat, proteases, and air, and stimulated BSH activity in at least two strains of gastric lactobacilli other than strain 100-100. Its ability to stimulate hydrolase activity was inhibited by N-ethylmaleimide. Attempts were unsuccessful to show that it binds bile salts and increases their uptake into the cells.
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