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An acid phosphatase catalyses hydrolysis of phosphate esters under acidic conditions; its lysosomal enzyme latency supplied evidence for lysosomes.

Christian de Duve investigated intracellular organization using biochemical fractionation. Work with Jacques Berthet examined a latent form of acid phosphatase, connecting enzyme accessibility with its subcellular association.

An enzyme can be present but poorly detected if a membrane limits substrate access. Comparing activity before and after disruption therefore helps distinguish low enzyme abundance from biochemical latency.^[ref]

A biochemist.^[ref]

Jacques Berthet coauthored research with Christian de Duve on the subcellular distribution and latency of acid phosphatase. The work links fractionation with measurements of enzyme accessibility.

Association with a cellular fraction does not by itself identify an enzyme's exact location. Latency and marker comparisons supply additional evidence about compartmentation.^[ref]

A biochemist.^[ref]

In the 1951 study by Jacques Berthet and Christian de Duve, liver from fasted rats was immediately chilled in an ice-cold isotonic chemical solution. The tissue was generally pressed through wire mesh; the weighed pulp was homogenized in cold $0.25\mathrm{mol}{\mathrm{L}}^{-1}$ sucrose using a glass Potter-Elvehjem homogenizer. Their acid phosphatase test concerned activity toward added glycerophosphate at pH $5$: the readout was substrate hydrolysis, rather than an image of a particle.^[ref]

Christian de Duve's retrospective describes successive centrifugation steps, separating centrifugation pellets and supernatants, and comparing enzyme distributions across the recovered fractions. Membrane disruption exposed previously inaccessible acid phosphatase activity, providing the crucial comparison with the membrane-preserving preparation. Joint fractionation patterns and release behavior of several acid hydrolases supported a shared population of digestive particles. By 1955, this evidence supported the lysosome concept.^[ref]

The inference was biochemical: a barrier restricted access to active enzymes. Co-sedimentation could confuse distinct particles; a crude mitochondrial fraction did not establish residence inside mitochondria. Lysosomal enzyme latency neither images an organelle nor determines its shape. Electron microscopy of enriched fractions supplied separate morphological evidence.^[ref]