Protein masked groups

The anomalously steep titration curve (pH 4 to 6) of collagen in 0.5 M NaCl (Bowes and Kenten, 1948) raises the possibility of the existence of masked groups in this protein. Drifts in pH could not be detected because attainment of equilibrium with the solid phase requires 3 days. The steepness is quite marked compared to that of wool (Steinhardt, Fugitt, and Harris, 1940a) in the same pH range thus effects due to the existence of separate phases are probably not responsible. The fact that only part of the lysine appears to be titrated lends strong support to the hypothesis of acid-labile masking in this protein (see Section II, 5 of this paper). 

A similar approach has been taken to prepare aryl phosphoramidates such as 99 [223], as prodmgs of SH2 domain analogs for Src/Lck inhibitors. The compounds exhibit low micromolar growth inhibition in Jurkat T cells, and undergo spontaneous hydrolysis with half-lives of approximately 30 min. The same masking groups have been applied in phosphonate 100 as a suspected SH2 domain blocker through inhibition of mitotic centromere-associated kinesin protein function in a panel of... 

Add a blocking agent, such as a non-relevant protein (e.g., BSA) to a final concentration of 1 percent to mask any nonspecific binding sites and to couple with any remaining reactive groups on the silica particle surface. This is important especially if a limiting amount of antibody was initially reacted with the particles in step 5. React for 30 minutes to 1 hour at room temperature. 

Goldberger, R., and C. B. Anftnsen Reversible masking of amino-groups in ribonuclease and its possible usefulness in the sjmthcsis of the protein. Biochemistry /. 401—405 (1962). 

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