ATP activation of protein degradation by extracts of crude and purified lysosomal preparations.

ABSTRACT

Activation of proteolysis by ATP was studied in lysates of crude and purified lysosomal preparations from liver and kidney at acid pH. In the crude system, from kidney, it was found that ATP activates proteolysis over a concentration range of 0.1-2 mM. Up to 4-fold activation was observed. GTP and CTP also activated proteolysis, but to a lesser extent. Proteolysis was inhibited by vanadate and molybdate. Fractionation of the kidney lysosomes on Percoll gradients produced two fractions containing lysosomal marker enzymes. Most of the acid phosphatase and the acid pyrophosphatase were found in the lighter band, while most of the beta-galactosidase and cathepsin activity was found in a more dense band. Proteolysis by lysates of both fractions was activated by ATP and inhibited by vanadate and molybdate. In the dense band proteolysis was also nearly totally blocked by pepstatin, and was enhanced by an inhibitor of pyrophosphatases, sodium fluoride. ATP also activates proteolysis in crude lysosomes from liver, but upon fractionation of this tissue it was found that all the lysosomal enzyme markers are present in the dense fraction obtained from the Percoll gradient. Again, proteolysis by lysates of the purified fractions was activated by ATP and inhibited by vanadate and molybdate. These data indicate that ATP can activate proteolysis at acid pH in a lysosomal milieu containing enzymes which also catalyze its breakdown. In the kidney there may be two lysosomal compartments which separate the enzymes catalyzing ATP breakdown from the proteolytic enzymes, but this is not essential for ATP activation as shown by the data from the liver and the crude lysosomal fractions.