Characterization of a conidial alkaline phosphatase from the thermophilic fungus Humicola grisea var. thermoidea
✍ Scribed by Luciana Baracchini Buainain; Marina Kimiko Kadowaki; Maria de Lourdes Polizeli; Héctor Francisco Terenzi; João Atilio Jorge
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 152 KB
- Volume
- 38
- Category
- Article
- ISSN
- 0233-111X
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✦ Synopsis
An extracellular alkaline phosphatase (EC 3.1.3.1) was purified from conidia of Humicola grisea var. thermoidea. The molecular mass of the purified native enzyme was estimated as 126 kDa by gel filtration. SDS-PAGE revealed a single polypeptide band of 63 kDa, suggesting that the native enzyme was a dimer of identical subunits. The pI of the enzyme was about 3.0. Optima of pH and temperature were 9.0 and 70 °C, respectively. In Tris-HCl buffer, pH 9.0, the enzyme was activated by MgCl 2 and strongly inhibited by ZnCl 2 , CoCl 2 , Al 2 Cl 3 , HgCl 2 , EDTA and β-mercaptoethanol. In contrast, in glycine buffer and at the same pH the enzyme was activated by ZnCl 2 and CoCl 2 , as well as by MgCl 2 . The enzyme was fully stable when incubated up to one hour at 65 °C without magnesium labilized the enzyme incubated at 65 °C or 70 °C. p-Nitrophenyl phosphate was the best substrate, but AMP, ADP, ATP and β-glycerophosphate also served as substrates. The remarkable ther- mostability exhibited by the purified alkaline phosphatase of H. grisea may be of interest for practical applications.
Alkaline phosphatases (orthophosphoric monoesterphosphohydrolase, EC 3.1.3.1) hydrolyze several monophosphate esters. Phosphomonoesterases are widely distributed in cells from animals, plants and microbial sources. However, little is known about the biochemical properties of the exocellular phosphatases from fungal spores (SAY et al. 1996), and in particular nothing is known about these enzymes from thermophilic fungi. One of the best characterized examples among filamentous fungi is the conidial alkaline phosphatase of