Estudo do comportamento acido-base de proteinas no sistema DMSO-Agua

AUTOR(ES)
DATA DE PUBLICAÇÃO

1989

RESUMO

Acid-base behaviour of lysozyme and ovalbumin was studied in an DMsO-water (7,0: 0,8 ml) system by catalytil thermometric titrimetry (CTT) and potentiometric titrimetry. In CTT, where acrylonitrile (4,0 ml) was employed as a thermometric indicator, 23,6±0,7 and 47,6±0,6 acid groups per moI of lysozyme and ovalbumin were determinated, respectívely. Camparison of these results with those abtained by potentiometric titrations of proteins denaturated in urea showed that guanidine goups (pKa =12,5 in water) are titrated in the DMSO-water medium. Both aluminum and glass were used as indicator electrodes in the potentiometric titrations. A nickel-chromium wire immersed in the titrant was used as reference electrode. The aluminum electrode did not provide satisfactary results in protein titrations, probably due to adsorption of proteins on the electrode surface. By employing the glass electrode, 11,4±0,5 and 52,3±1,5 acid groups, and 22,7±0,8 and 97,0±2,1 total groups per mol of lysozyme and ovalbumin were determinated, respectively. These results show that the guanidine groups of lysozyme are weaker acids than those of ovalbumin, since they are determinated only by CTT.

ASSUNTO(S)

proteinas ion hidrogenio - concentração lisozima

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