... restriction to Lck accessing certain tyrosine residues of the protein chain Our studies have determined the efficiency of phosphorylation of each of the six f ITAM tyrosines by PTK Lck, from which ... vitro phosphorylation by Lck, confirmed tyrosine 1N to be the first phosphorylated Differences arising in the order of phosphorylation of the subsequent tyrosines in the whole cTCRf chain in vitro, ... rate-limited by ATP concentration The levels of incorporation of 32P into the peptide were used to calculate the kinetics of phosphorylation by Lck at each tyrosine, and from these an order of phosphorylation...