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The behavior of isolated zymogen granules: pH-dependent release and reassociation of protein

1971; Elsevier BV; Volume: 241; Issue: 2 Linguagem: Inglês

10.1016/0005-2736(71)90055-1

1879-2642

Stephen Rothman,

Enzyme Production and Characterization

1. The release of chymotrypsinogen, trypsinogen, and amylase from zymogen granules which were isolated from rat pancreas was studied as a function of pH. Enzyme release was lowest at slightly acid pH and increased progressively as pH was raised above neutrality. When pH was plotted against the percentage of enzyme released from the granules different curves were formed for different enzyme species. 2. At alkaline pH's enzyme release was essentially complete within the time required to separate the granules from the suspending medium by centrifugation, but release kinetics could be followed in “unstable” acid conditions (pH 4.5). At pH 4.5 a time-dependent release of trypsinogen could be followed under conditions in which the homologous protein, chymotrypsinogen, was completely retained within the granules. 3. Granule contents which were released at alkaline pHs could be reassociated or reaggregated when the pH of the suspension was again made acidic. As much as 90 % of the original protein content of the granules could be reassociated. This pH-dependent reassociation required the presence of granule membrane and perhaps a non-secreted lipoidal moiety as well. 4. These experiments support the view that the zymogen granule is either internally ordered or that different granules contain different enzymes or groups of enzymes. Furthermore, the digestive enzymes appear to associate in some manner with molecules forming part of the granule membrane. A hypothesis is proposed to explain the results in which polymers of a particular digestive enzyme form as a result of the association of a molecule of this enzyme with granule membrane.