EVIDENCE FOR ACIDITY OF PRELYSOSOMAL AUTOPHAGIC ENDOCYTIC VACUOLES (AMPHISOMES)

[C-14]Lactose electroinjected into isolated rat hepatocytes is normally autophagocytosed, transferred to lysosomes and degraded by lysosomal beta-galactosidase, but at high concentrations of asparagine the transfer is inhibited and lactose accumulates in prelysosomal autophagic/endocytic vacuoles (amphisomes). The accumulation can be prevented by addition of yeast beta-galactosidase, which is transferred to the lactose-containing vacuoles by endocytosis. Propylamine, a weak base capable of neutralizing acidic vacuoles, protects autophagocytosed lactose against both endogenous and exogenous beta-galactosidase, suggesting that amphisomes, like lysosomes, have an acidic internal environment.