THERMAL AND PH STABILITIES OF ALKALINE-PHOSPHATASE FROM BOVINE INTESTINAL-MUCOSA - A FTIR STUDY

The inactivation of alkaline phosphatase (AP) from bovine intestinal m ucosa caused by lowering the p(2)H from 10.4 to 5.4 or by increasing t he temperature from 25 degrees C to 70 degrees C were not followed by significant FTIR changes, indicating that the native conformation of A P was preserved under these conditions. Further decrease of p(2)H from 5.4 to 3.4 leaded to small infrared spectral changes of AP in the ami de I' and amide II regions that were similar to the infrared spectral changes of AP induced by raising the temperature from 70 degrees C to 80 degrees C. The increase of temperature from 70 degrees C to 80 degr ees C promoted the formation of intermolecular beta-sheets at the expe nse of some alpha-helix structures as evidenced by the appearance of t he 1684 cm(-1) and 1620 cm(-1) component bands and the disappearance o f the 1651-1657 cm(-1) component band. This conformational change was followed by a sharp increase of the H-2/H exchange rate. CD spectra co nfirmed the FTIR results and were very sensitive to the variation of a lpha-helix content while FTIR spectra were more receptive to the chang es of beta-sheet structures.