Thermostabilization of Bacillus amyloliquefaciens α-amylase by chemical cross-linking

Study of gherkin lactase in cell culture and in seedlings

A synthetic substrate replacing lactose has facilitated application of a simple, rapid and sensitive method for the identification and determination of extracellular and intracellular gherkin lactase. The intracellular enzyme activity was estimated from the cell suspension, while the extracellular enzyme activity was established within the cell free cultivation medium. A suspension of gherkin cells was permeabilized by Tween 20, or Tween 80, or hexadecyltrimethyl ammonium bromide, or hexadecylpyridinium chloride or ethanol added one at a time and then immobilized by glutaraldehyde. The highest lactase activity was at pH 4.8 at a temperature of 55°C. The hydrolysis of substrate was linear for 4.5h and reached 60% conversion. The cells had high lactase activity and good stability. During long-term storage they demonstrated convenient physico-mechanical properties.

Thermal aggregation of a model allosteric protein in different conformational states

Protein aggregation is of crucial importance in a wide variety of situations. High temperatures, combined with other denaturing conditions, have been used very extensively to decipher some of the fundamentals related to formation of amorphous and fibrillar protein aggregates. The present study reports on the dependency of thermal aggregation of bovine liver glutamate dehydrogenase (GDH), a well-characterized allosteric enzyme, on its conformational state. The initial phases of thermal aggregation of this protein was followed in the presence of a number of well-known allosteric ligands. Positive effectors were found to decrease the rate and extent of aggregation in a concentration dependent manner, while negative effectors did the reverse. ADP, one of the most characterized GDH activators was found to stabilize a specific protein conformation resulting in loss of propensity to aggregate. The importance of this observation related to control of protein-protein interactions leading to protein aggregation is discussed.

Stabilization of Bacillus licheniformis alpha-amylase by specific antibody which recognizes the N-terminal fragment of the enzyme

Bacillus licheniformis alpha-amylase (BLA) is an industrially important extracellular enzyme with a number of applications. In the present work, an investigation was carried out on the tryptolytic digestion of BLA which produced two fragments, TF18K and TF38K, and no further fragments could be seen after 6h incubation of BLA with trypsin. The fragments were isolated by preparative gel electrophoresis and reverse phase HPLC. The N-terminal sequencing of fragments showed that trypsin attacks on Arg(127)-Val(128) peptide bond in BLA. Intrinsic and acrylamide quenching fluorescence experiments and Far-UV circular dichroism studies showed that substantial changes in the secondary and tertiary structures of the TF18K and TF38K have occurred. Subsequently, polyclonal antibody was raised against TF18K. After purification of the antibody by protein A Sepharose, thermal stability of BLA in the presence of this antibody was determined. Results showed that the presence of antiTF18K leads to significant stabilization of BLA. For example, after 30 min incubation at 90 degrees C, residual activity of the enzyme in the presence of antibody (40 microg/ml) was determined as 40% while the enzyme showed no activity in the absence of antibody after incubating in the same condition. In addition, it has been proved that calcium enhances the thermal stability of BLA and a synergistic stabilization of BLA has been seen with antiTF18K and calcium, simultaneously.