Purification and characterization of two alkaline, thermotolerant alpha-amylases from Bacillus halodurans 38C-2-1 and expression of the cloned gene in Escherichia coli

A newly isolated strain, 38C-2-1, produced alkaline and thermotolerant alpha-amylases and was identified as Bacillus halodurans. The enzymes were purified to homogeneity and named alpha-amylase I and II. These showed molecular masses of 105 and 75 kDa respectively and showed maximal activities at 50-60 degrees C and pH 10-11, and 42 and 38% relative activities at 30 degrees C. These results indicate that the enzymes are thermotolerant. The enzyme activity was not inhibited by a surfactant or a bleaching reagent used in detergents. A gene encoding alpha-amylase I was cloned and named amyI. Production of AmyI with a signal peptide repressed the growth of an Escherichia coli transformant. When enzyme production was induced by the addition of isopropyl beta-D(-)-thiogalactopyranoside in the late exponential growth phase, the highest enzyme yield was observed. It was 45-fold that of the parent strain 38C-2-1.     

Cassava (Manihot esculenta Crantz of cv. KU50) peroxidase and its potential for the detection of some thiol compounds based on the inhibitory effect of 3,3′,5,5′-tetramethylbenzidine oxidation

Cassava peroxidase (CSP) isolated from cassava leaves (Manihot esculenta Crantz of cv. KU50) was purified by DEAE and concanavalin-A column chromatography. CSP was a haem-containing cationic glycoprotein with the molecular weight of 38 and 44 kDa determined by MALDI-TOF-MS. Its kinetic catalysis in the presence and absence of some thiols were investigated and compared to those of horseradish and soybean peroxidases by using urea hydrogen peroxide (UHP) and 3,3′,5,5′-tetramethylbenzidine (TMB) as substrates. Inhibitory effects of some pesticides containing thiol groups such as thiosemicabazide, thiourea and thiophanate-methyl on TMB oxidation were graphically demonstrated their ability to be either competitive or noncompetitive inhibitors, depending on their properties. The degrees of inhibition were expressed as K_i and IC₅₀ values. The applicable range for the detection of thiosemicabazide in solution was found to be in the range of 10–100 μM, whereas those of thiourea and thiophanate-methyl were 40–400 μM and 10–460 μM, respectively. On the contrary, the inhibitory effects of some phenolic pollutants; 4-nitrophenol, 4-phenylphenol and pentachlorophenol on TMB oxidation were not significantly observed and the phenomenon was discussed.