Bovine protein tyrosine phosphate

Two protein tyrosine phosphatases (PTPases) have been studied with hybrid potentials — the catalytic domain of human PTPIB [89] and the bovine PTPase (BPTP) [90]. These proteins have similar active centers and there is an invariant catalytic cysteine amino acid residue. Hillier et al characterized the transition state for the phosphate hydrolysis by PTPIB (with a dianion phosphate) using a PM3/MM potential but keeping the protein matrix and some of the QM atoms fixed. They found a dissociative mechanism in which the cleavage of the P-0 bond occurred before the formation of the S-P bond. The breaking of the P-O bond was determined to be the rate limiting step in agreement with kinetic... 

In this work, the solutions of human serum albumin (HSA) (>96%, Sigma) and of bovine serum albumin (BSA) (>98%, MP Biomedicals) in a phosphate buffer (0.01 M, pH 7.4) have been used. The proteins concentrations were lO- (absorption spectra measurement) and 10- M (fluorescence measurement at the nanosecond laser fluorimeter). All of the experiments were performed at a temperature of 25 1 °C. The structure and biological functions of HSA and BSA can be found in (Peters, 1996). Tryptophan, tyrosine, and phenylalanine (with relative contents of 1 18 31 in HSA and 2 20 27 in BSA) are the absorption groups in these proteins (as in many other natural proteins). The tyrosine fluorescence in HSA and BSA (as in many other natural proteins) is quenched due to the effect of adjacent peptide bonds, polar groups (such as CO, NH2), and other factors, and phenylalanine has a low fluorescence quantum yield (0.03) (Permyakov, 1992). Therefore, the fluorescence signal in these proteins is determined mainly by tryptophan groups. In that case the fluorescence, registered in nonlinear and kinetic laser fluorimetry measurements, correspond to tryptophan residues (this fact will be used in Section 6.1). 

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