Fructose 1,6-bisphosphatase: the role of lysosomal enzymes in the modification of catalytic and structural properties.

Seasonal variations in the properties of rabbit-liver fructose 1,6-bisphosphatase have now been linked to corresponding changes in the levels of proteolytic activity in the liver extracts. Incubation of native fructose 1,6-bisphosphatase with purified liver lysosomes causes a 3-fold increase in catalytic activity at pH 9.2, with a smaller, and variable, decrease in activity tested at pH 7.5. These changes in catalytic properties are accompanied by the appearance of a smaller subunit, as was previously reported for the enzyme treated with subtilisin. AMP, a negative modulator of fructose bisphosphatase activity, protects against this action of lysosomes. This proteolytic modification of fructose bisphosphatase by lysosomal enzymes may play a role in the modulation of gluconeogenesis.