Journal
LIMNOLOGY AND OCEANOGRAPHY
Volume 50, Issue 5, Pages 1345-1351Publisher
AMER SOC LIMNOLOGY OCEANOGRAPHY
DOI: 10.4319/lo.2005.50.5.1345
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We examined how ultraviolet radiation (UVR) affects the activity of alkaline phosphatase (APase), a common extracellular enzyme. APase activity declined up to 57% under UVR exposure and decreased more often under ultraviolet A than ultraviolet B exposure, indicating that most of the observed decrease did not occur through direct enzyme inactivation. Enzyme activity in the particulate fraction (> 0.22 mu m) was less susceptible to UVR than activity in the total or dissolved fractions, suggesting that attachment to the cell surface may convey some protection against UVR-induced inactivation. Samples that were 0.22-mu m filtered before being subjected to radiation treatments often showed increased enzyme activity, especially in the photosynthetically active radiation-only treatment, indicating reactivation of APase in the absence of de novo production of the enzyme. Decreases in APase can be severe near the lake surface, suggesting that UVR-induced variations in APase activity might contribute to microscale variations in nutrient availability and community composition.
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