We have studied the in situ coordination reaction of porphyrin molecules, particularly protoporphyrin IX (H2PPIX), with copper substrate atoms in ultrahigh vacuum conditions with a combination of X-ray photoelectron spectroscopy and scanning tunneling microscopy. We show that these protoporphyrin IX molecules deposited on Cu surfaces, as Cu(110) and Cu(100), form metalloprotoporphyrin IX (CuPPIX) by incorporation of Cu atoms from the surface already at room temperature. We have followed this reaction as a function of temperature and we have determined intermediate situations at lower temperatures where the physisorbed macrocycle rings present a tendency to establish hydrogen bonding between molecules.