  Although the amino acid tyrosine is among the main building blocks of life,
its photochemistry is not fully understood. Traditional theoretical simulations
are neither accurate enough, nor computationally efficient to provide the
missing puzzle pieces to the experimentally observed signatures obtained via
time-resolved pump-probe spectroscopy or mass spectroscopy. In this work, we go
beyond the realms of possibility with conventional quantum chemical methods and
develop as well as apply a new technique to shed light on the photochemistry of
tyrosine. By doing so, we discover roaming atoms in tyrosine, which is the
first time such a reaction is discovered in biology. Our findings suggest that
roaming atoms are radicals that could play a fundamental role in the
photochemistry of peptides and proteins, offering a new perspective. Our novel
method is based on deep learning, leverages the physics underlying the data,
and combines different levels of theory. This combination of methods to obtain
an accurate picture of excited molecules could shape how we study photochemical
systems in the future and how we can overcome the current limitations that we
face when applying quantum chemical methods.
