Role of neuraminic acid in the heterogeneity of alkaline phosphatase in sheep brain.

1. Two alkaline phosphatase fractions from sheep brain obtained by DEAE-cellulose column chromatography were shown to be associated with different concentrations of NANA (N-acetylneuraminic acid). Enzyme II contains nearly three times as much NANA as does enzyme I. 2. Partial removal of NANA by neuraminidase digestion from these alkaline phosphatase fractions has different effects on their chromatographic properties. Though the enzymic release of NANA has no effect on the elution pattern of enzyme I from a DEAE-cellulose column, such a treatment shifts the elution pattern of enzyme II towards that of enzyme I. 3. However, this change in the elution pattern of enzyme II as a result of the removal of NANA does not produce any change in the kinetics of this fraction, and the differences between enzyme I and enzyme II with respect to their substrate affinities and K(i) for phosphate inhibition are maintained even after the removal of NANA. 4. Results indicate that NANA is not the only factor responsible for the heterogeneity of alkaline phosphatase in sheep brain and enzyme I is not the result of the removal of NANA from enzyme II.