An isoelectric focusing study of acid phosphohydrolases in rat liver lysosomes

The differentiation of rat liver lysosomal acid phosphatase, acid ATPase, acid phosphodiesterase, acid ribonuclease, and acid deoxyribonuclease was studied by isoelectric focusing. To prevent autolytic digestion, inhibitors of cathepsins and neuraminidase were used. The proportion of acidic forms of acid phosphatase, acid ATPase and acid phosphodiesterase was increased by the use of extraction medium containing 0.05% Triton X-100. To investigate the identity of acid ATPase and acid phosphodiesterase, the relative activities among the multiple forms of these enzymes, the acid phosphodiesterase/acid ATPase ratio at each activity peak, and the degree of enzyme inhibition by p-chloromercuriphenyl sulfonic acid were estimated. The results suggest that acid ATPase is not identical with acid phosphodiesterase. With extraction medium free of Triton X-100, acid ribonuclease appeared in two forms. However, in addition to these forms, a new form of this enzyme with a more acidic pI (4.22) emerged when extraction medium containing 0.05% Triton X-100 was used. The major peak of acid deoxyribonuclease with pI=8.40-9.39 was obtained regardless of the extracting method.