sentences:  Its importance can be further demonstrated by the fact as much as 1% of all secreted and membrane tyrosine residues are found to be sulfated.Within the last two years, using the crystallized structure of the catalytic region of TPST-2 and different experiments other methods using mass spectrometry methods have come to propose two separate mechanisms.A two-site ping-pong mechanism for TPST and the tyrosine sulfating has been proposed.