PROTEIN IMMOBILIZATION BY AMINOLYSIS OF CELLULOSE XANTHATE ESTERS

P-Nitrobenzyl cellulose xanthate (CelXNB) was obtained with a degree of substitution (DS) in the range 0.5-3. The first-order rate constant for hydrolysis of CelXNB at 25-degrees-C, extrapolated to zero buffer concentration, is hydroxide ion catalysed, whereas the water-catalysed path is about 2000 times faster than that observed for p-nitrobenzyl ethylxanthate (EXNB), probably owing to the highly ordered cybotactic region of cellulose. Aminolysis of CelXNB produces the corresponding thioncarbamate ester; for simple alkylamines, the second-order rate constants are similar to those obtained for EXNB. The second-order rate constants at pH 11 for immobilization of bacterial alpha-amylase and bovine serum albumin were 13.4 and 1121 mol-1 s-1, respectively, unexpectedly high values when compared with simple alkylamines, even considering the concentration of external reactive groups of the proteins. CelXNB with low DS should release 1 mol of p-nitro-alpha-toluenethiol for every mole of protein that becomes immobilized. The net weight increase of the cellulose matrix allows the calculation of the absolute molecular weight of the protein. Preliminary results support this assumption.