So this is the Thymine pyrophosphate, and it is actually attached onto the enzyme. Now, what happens in step one is this transforms from a poor nuclear file to a good nuclear file. And what happens is we have an ionization reaction taking place in which this hydrogen ion basically departs and it leaves a full negative charge on this carbon. So we form a carbonate intermediate molecule, the Thiamine Pyrophosphate carbonate. Now, as a result of the presence of the two electrons on this carbon atom, this becomes a good nuclear file. And that and now it acts as a strong nuclear file and attacks this electrophile.