Journal
SCIENTIA AGRICOLA
Volume 66, Issue 5, Pages 634-642Publisher
UNIV SAO PAOLO
DOI: 10.1590/S0103-90162009000500008
Keywords
Selenastrum capricornutum; algae; enzyme; metal; toxicity
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Funding
- Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)
- Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq)
- Empresa Brasileira de Pesquisa Agropecuaria (EMBRAPA)
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Pseudokirchneriella subcapitata is a unicellular green algae widely distributed in freshwater and soils. Due to its cosmopolitan characteristic, its use is recommended by national and international protocols in ecotoxicity studies. The alteration of phosphatase activities by agriculture pollutants like heavy metals has been extensively used as a biomarker in risk assessment and biomonitoring. In this study, we compared the extraction of acid phosphatase from P. subcapitata by different procedures and we studied the stability, substrates specificity, kinetics and the effect of Hg2+ in the crude extract. The freezing and thawing technique associated with probe sonication was the most suitable method of extraction. The enzyme was stable when frozen at -20 degrees C for at least six months, showed an optimum pH of 5 and a Km value of 0.27 mM for p-nitrophenylphosphate (pNPP) as substrate. Some natural organic substrates were cleaved by a similar extent as the synthetic substrate pNPP. Short term exposure (24 hours) to Hg2+ had little effect but inhibition of the specific activity was observed after 7 days with EC50 (concentration of Hg2+ that promotes 50% decrease of specific activity) value of 12.63 mu M Hg2+.
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