The selective role of cathepsins B and D in the lysosomal degradation of endogenous and exogenous proteins

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Abstract
A selective inhibitor of cathepsin B, a derivative of E‐64 (compound CA‐074), and pepstatin‐asialofetuin, a potent inhibitor of cathepsin D, were used for an in vivo study of the selective role of these proteinases in lysosomal proteolysis. Administration of compound CA‐074 or pepstatinasialofetuin to rats caused only a slight shift of the lysosomal density and no increase in sequestered enzymes in the autolysosomal fraction, although cathepsin B or D activity in the liver was markedly inhibited. These treatments also had little effect on the inhibition of the degradation of endocytosed FITC‐labeled asialofetuin. In contrast, leupeptin treatment caused marked inhibition of lysosomal degradation of endogenous and exogenous proteins. These results suggest a small contribution of cathepsins B and D to the initiation of lysosomal proteolysis.