Some months before @robField’s tweet setting off the train that led to the Eu sensor that discriminates PAP/PAPS, Ed Yates and myself were having a curry with Dulce Papy-Garcia from UPEC, who had examined one of our PhD students. A matter we discussed at length was ‘why sulfate’. That is, why does biology use both sulfate and phosphate to modify post synthesis proteins, polysaccharides and other molecules. We didn’t come up with an answer, but the conversation led Ed and myself to consider that the question merited exploration.
This we thought would be a simple matter.
It turned out to be one of the most difficult papers Ed and myself have written, to the extent that after N drafts (where N is a significantly larger number than either of us had experienced in any previous writing exercise) and too many summers we still had nothing satisfactory. So, we cunningly inveigled two colleagues, Tim Rudd from NIBSC and Marcelo Lima from Keele to join us on what we advertised as the sunny beach of sulfate and phosphate, but which in reality was a rather dank quagmire. There is though something about strength in numbers, and with very helpful input from Steve Butler in Loughborough, we arrived at what we considered a satisfactory synthesis. Happily, the reviewers concurred, and the paper is now published at Royal Society Interfaces, “Phosphorylation and sulfation share a common biosynthetic pathway, but extend biochemical and evolutionary diversity of biological macromolecules in distinct ways”.
This is by no means the last word on the matter, but along with some previous thoughtful papers we cite (if we have missed one, please let me know) it provides some ideas that may help us to understand why biology co-opted particular elements from the inorganic world to perform groups of functions vital to life as we know it now.
Ferniglab Blog 
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