Chaperone-like activity of β-casein and its effect on residual in vitro activity of horseradish peroxidase

In this study, the residual activity horseradish peroxidase was used as a novel marker of chaperone-like activity of -casein under elevated temperature. It was shown that -casein does affect residual activity of horseradish peroxidase (HRP) depending on the concentration and molar ratio between proteins. Incubating HRP (0.1mgmL(-1)) for 10min at 72 degrees C resulted in residual activity of 59 +/- 5%, while addition of 1mgmL(-1) -casein resulted in increase in residual activity up to 85 +/- 1%. Increased residual activity is not merely attributed to an effect of higher total protein concentration, as similar experiment with bovine serum albumin resulted in residual activity of horseradish peroxidase that was significantly lower than without any addition. The effect of -casein on HRP disappears when pH is below the isoelectric point of -casein. It was also proven by light scattering studies that -casein interacts with horseradish peroxidase when the temperature was increased from 25 to 70 degrees C whereas interactions seem to cease when temperature was lowered back to 25 degrees C. This study highlights how specific proteins can influence enzyme activity, which is of potential importance for various industries such as enzyme manufacturers and food industry.