Evidence for the selective release of lysosomal proteinases in fasted rabbits

The enzyme responsible for the conversion of "neutral" to "alkaline" fructose 1,6-bisphosphatase (EC 3.1.3.11) by removal of a 7000 dalton peptide (converting enzyme, Proteinase I) has been shown to be localized in rat liverlysosomes. Lysosomes also contain a specific proteinase (Proteinase II) that catalyzes the release of a small peptide from the NH2-terminus of the native subunits. In fasted rabbits Proteinase II is released into the cytoplasm, together with Cathepsin A, but Proteinase I remains associated with the lysosomal fraction. Increased osmotic fragility of liver lysosomes in fasted rabbits has also been observed, but this increased fragility does not result in the release of Proteinase I. The appearance of Proteinase II in the cytoplasm may be due either to its selective release from the lysosomes, without release of Proteinase I, or its localization in a different lysosomal fraction. Changes in lysosomal structure induced by fasting may play a dual role in : 1) the mobilization of amino acids for gluconeogenesis and 2) the modulation of activity of gluconeogenic enzymes.