Abstract

The α-amylase of marine Pseudomonas sp. K6-28-040 was purified through a series of three steps and the purity of enzymes was checked by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The results showed that, the enzyme was purified 4.7-fold with a specific activity of 134.6 U/mg protein and a yield of 44%. When it was subjected to SDS-PAGE, a single band near 58 kDa appeared.The optimum temperature and pH were 50°C and 7.0, respectively. The addition of Ca²⁺, Mn²⁺ and Co²⁺ could improve the enzyme activity, while Cu²⁺, Hg²⁺, Fe³⁺and Al³⁺ decreased the activity. The enzyme was inhibited by ethylenediaminetetraacetic acid (EDTA), ethylenebis(oxonitrilo)]tetra-acetate (EGTA), SDS and dimethyl sulfoxide (DMSO), but was not affected by phenylmethane-sulfonyl fluoride (PMSF) and 1,4-dithiothreitol (DTT). K_m and V_maxvalues of the purified enzyme for soluble starch were 1.73 ± 0.3 mg/ml and 1.24 ± 0.02 mg/ml/min, respectively. The degradation ability of wild type α-amylase on starch granules was examined by thin layer chromatography. The final purified enzyme had an isoelectric point of 7.5-7.8 and α-helix of 28%, β-sheet of 32% and random coil of 40%.

Key words: α-Amylase; Pseudomonas sp., purification, enzyme characterization.

Abbreviation

EDTA, Ethylenediaminetetraacetate; EGTA,ethylenebis(oxonitrilo)]tetra-acetate; SDS, sodium dodecyl sulphate; DMSO,dimethylsulfoxide; PMSF, phenylmethane-sulfonyl fluoride; DTT, 1,4-dithiothreitol;CD, circular dichroism; TLC, thin-layer chromatography; IEF, isoelectric focusing;pI, isoelectric point