I see people writing "Glucuronyl C5-epimerase", "Glucuronyl C-5-epimerase", "Glucuronyl-C-5-epimerase" and "Glucuronyl C5 epimerase", which one is correct? Is there a naming convention?
I have not found this particular enzyme in Enzyme Nomenclature. However, following the Recommendations of the Nomenclature Committee of the International Union of Biochemistry and Molecular Biology, the name should be glucuronyl 5-epimerase. See also this sublist for some analogous names of other epimerases.
In addition to Loong’s answer which includes the formally correct way to write it: if you wish to unambiguously indicate that a carbon atom is epimerised, the only possible choices are those that leave no space between the symbol for carbon and the digit. Atoms are number-named by writing the element symbol directly followed by their number without hyphen or space. So the atom in question is C5, meaning we have a C5-epimerase.
: Which is superfluous since carbon atoms are practically the only atoms ever epimerised.