Thousands of enzymes are the chemists of all cells, allowing life to exist. The special proteins that contain the chemical structures that allow for enzymatic activities transform simple molecules into the complicated macromolecules such as DNA, proteins, polysugars, lipids, etc. Enzymes catalyze the synthesis and degradation of molecules, perform metabolic and energetic tasks and protect our cells from both internal and external dangers. Understanding the precise mechanisms of enzyme catalysis is almost impossible with knowledge of their three-dimensional structures. We are interested in all aspects of enzymes function: how to they fold and assemble? How do they perform their catalytic function? How do they bind substrates, inhibitors, analogs, co-factors and solvent molecules? What happens if certain amino acids are changed (mutations)? How did they evolve from more primitive proteins? Many of these questions can be answered by determining the structures of enzymes by X-ray crystallography. We are now working on an important enzyme called Tyrosinase, which catalyzes the transformation of tyrosine to quinones, that aggregate to make melanin – the ubiquitous coloring agent found in skin, hair, eyes and elsewhere. In collaboration with Prof. Ayelet Fishman of the Faculty of Biotechnology and Food Engineering of Technion, we have explored this enzyme, isolated in Ayelet’s lab from a soil bacterium called B. megaterium. We have solved this enzyme in its active form, showing exactly how it’s substrates bind, how it is inhibited by compounds used in cosmetics, how critical copper ions are uptaken and much more.