Fig. 5: Model of the secretion and function of the four alkaline phosphatase families.

This figure illustrates the distinct secretion mechanisms employed by the four purified alkaline phosphatases from Alteromonas mediterranea. The Sec pathway utilized by PhoA (green) and PafA (pink) and the Tat pathway employed by PhoD (blue) and PhoX (purple). These differential secretion strategies suggest an advantage for PhoD and PhoX in acquiring the cofactor iron, as the Tat pathway enables these enzymes to fold before secretion. Conversely, PhoA and PafA rely on external environmental concentrations of their cofactor zinc. The lower part of this figure presents enzymatic turnover rates for four different substrates: P-monoester, P-diester, P-triester, and sulfate monoester. To visualize differences in the lower ranges, the values have been transformed to a logarithmic scale. All four purified enzymes exhibit enzymatic activities with all substrates, except for PafA, which does not show activity with P-monoester. Created in BioRender. Saavedra, D. (2024) https://BioRender.com/ b23b787.