Determination of the critical molar mass of ovalbumin oligomers degraded by ultrasound

Abstract

An experimental method has been developed which enables the determination of the critical molar mass (Mmc) of ovalbumin oligomers degraded by ultrasound of known frequency. To test the validity of the Mmc postulate, a series of ovalbumin oligomers was prepared by the radiolytic cross-linking of 1% solutions of ovalbumin monomer dissolved in 50 mM Na/K-phosphate buffer pH 7.0 saturated with N2O. Under these conditions, irradiation with 5 kGy from a Co-60 source, yielded ovalbumin dimers, trimers, tetramers, and higher order oligomers. On the basis of the results obtained with the ovalbumin oligomers, it was concluded that for ultrasound of 23 kHz frequency and 5 mu m amplitude, the Mmc was 274000 +/- 14000 g/mol. Our results confirmed that the two postulates in the chemistry of polymer degradation by ultrasound are valid when ovalbumin oligomers are used as substrates, i.e., (1) that the higher the molar mass of the original macromolecule, the faster is its degradation rate, and (2) that a lower molar mass limit (LMmL) exists below which the macromolecules are resistent to further degradation.