Abstract
Alkaline phosphatase (AP) enables marine phytoplankton to utilize dissolved organic phosphorus (DOP) when dissolved inorganic phosphate (DIP) is depleted in the ocean. Dinoflagellate AP (Dino-AP) represents a newly classified atypical type of AP, PhoAaty. Despite While being a conventional AP, PhoAEC is known to recruit Zn2+ and Mg2+ in the active center, and the cofactors required by PhoAaty have been contended and remain unclear. In this study, we investigated the metal ion requirement of AP in five dinoflagellate species. After AP activity was eliminated by using EDTA to chelate metal ions, the enzymatic activity could be recovered by the supplementation of Ca2+, Mg2+ and Mn2+ in all cases but not by that of Zn2+. Furthermore, the same analysis conducted on the purified recombinant ACAAP (AP of Amphidinium carterae) verified that the enzyme could be activated by Ca2+, Mg2+, and Mn2+ but not Zn2+. We further developed an antiserum against ACAAP, and a western blot analysis using this antibody showed a remarkable up-regulation of ACAAP under a phosphate limitation, consistent with elevated AP activity. The unconventional metal cofactor requirement of Dino-AP may be an adaptation to trace metal limitations in the ocean, which warrants further research to understand the niche differentiation between dinoflagellates and other phytoplankton that use Zn–Mg AP in utilizing DOP.
Highlights
In marine ecosystems, the availability of P is critical to the growth of phytoplankton
The metal ion requirement analysis was performed on crude protein extracts of A. carterae, K. mikimotoi, A. pacificum, P. minimum and F. kawagutii collected under the P-depleted condition
To exclude the possibility that the apparent lack of Alkaline phosphatase (AP) activation by Zn2+ was due to a toxic effect of overdose, the commercialized calf intestinal alkaline phosphatase (CIAP) was used as a control in the assay
Summary
The availability of P is critical to the growth of phytoplankton. P is often found to be the limiting nutrient of the primary productivity in the ocean [1,2]. P is present in both inorganic and organic forms, among which dissolved inorganic phosphorus (DIP) as the preferred form for phytoplankton is quickly consumed and found at a low concentration in the euphotic zone [3]. Dissolved organic phosphorus (DOP) is relatively abundant in the euphotic zone. DOP mainly occurs in two forms: The major form phosphoesters and the less abundant form phosphonates [4,5]. When facing the DIP limited condition, phytoplankton are able to utilize a broad spectrum of phosphoesters to meet their cellular P requirement and sustain their primary production [6,7]
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