I think I have found a bug in the human ec model (which does not exist in Human1).
In Human-GEM, reaction HMR_7197 looks like this:
[protein][c] + serine[c] => [protein]-L-serine[c] + H2O[c]
But, in the ec model, it looks like this when I do constructEquations:
[protein][c] + serine[c] => L-serine[c] + H2O[c]
So, the [protein]- part of the L-serine seems to have gone missing. We suspect that it has something to do with the square brackets, or potentially the word "protein".