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Lysosomal Enzyme Activities in the Regenerating Rat Liver¹

Fondation Curie-Institut du Radium, Université de Paris-Sud, Bâtiment 111, 91405 Orsay, France

The activity of four lysosomal enzymes (hyaluronidase, ß-N-acetylglucosaminidase, acid phosphatase, and cathepsin D) was studied in aqueous extracts of the light mitochondrial fraction of regenerating male rat liver. This tissue was chosen as a model for normal cell division in vivo. In the first wave of division, 40 to 50% of the cells divide synchronously. Activities were measured at 0, 9, 18 (end of G₁ phase), 24 (S phase), and 30 hr (mitosis) and during regeneration, 4 and 11 days after partial hepatectomy. Activities were related to fresh tissue weight, to cellular DNA, and to protein content of the extracts.

At 9 hr, there was an important increase in hyaluronidase and cathepsin D activities (these two enzymes act upon macromolecules); ß-N-acetylglucosaminidase and acid phosphatase activities were only slightly increased. At the end of the G₁ phase, 40 to 50% of the activity of all four enzymes was lost, which might indicate complete loss of activity in cells undergoing division. This depletion persisted until mitosis was complete. Four days later, there was a slow restoration of enzyme activities; after 11 days, hyaluronidase and cathepsin D exhibited about 80% of their initial activity, whereas ß-N-acetylglucosaminidase and acid phosphatase only regained about 50%.

These results show that the lysosomal system perhaps plays some role in cell division.

¹ This research was supported in part by a grant from the Lady Tata Memorial Trust, London, England.

² To whom requests for reprints should be addressed.

Received 6/16/76. Accepted 11/ 1/76.