Acid nucleases of the bovine adrenal medulla

Protease and ribonuclease activities in bovine pituitary lobes

1. Acid and alkaline protease activities in bovine anterior and posterior pituitary lobes were reinvestigated by measurement of u.v. and Folin-Ciocalteu colour values of trichloroacetic acid-soluble digestion products of denatured haemoglobin. 2. Both lobes of the pituitary gland contain a cathepsin with a pH optimum at 3.8. 3. When release of u.v.-absorbing material was used as the assay there was also an optimum at pH8.3-9.7, but this proved to be due to the release of nucleosides from an endogenous substrate. 4. The presence of a ;cyclizing' ribonuclease active at alkaline pH on endogenous RNA was confirmed by the inhibitory effects of phosphate, arsenate and bentonite. The activity was unaffected by heat, EDTA or metal ions. The enzyme also acted on exogenous RNA. 5. A purified preparation of neurosecretory granules from fresh bovine posterior pituitary lobes was free from alkaline ribonuclease activity. Most of the activity present in the tissue was recovered in the supernatant plus microsomal material. 6. The distribution of RNA did not follow that of the alkaline ribonuclease.

The localization of lysosomal enzymes in chromaffin tissue

1. An homogenate of bovine adrenal medulla contains significant amounts of six acid hydrolases: acid ribonuclease, acid deoxyribonuclease, cathepsin, acid phosphatase, beta-glucuronidase and arylsulphatase. Most of the activity of each enzyme could be sedimented in the large-granule fraction at 242,000 g-min.2. Differential centrifugation indicated the presence of three populations of particles, which sedimented at slightly different rates; these are, in order of decreasing sedimentation rate, mitochondria, particles containing the acid hydrolases, and chromaffin granules.3. The three types of particle could be separated by ultracentrifuging the large-granule fraction in a sucrose density gradient. Most of the activity of each hydrolase was recovered in a layer intermediate between those formed by mitochondria and chromaffin granules.4. The large-granule fraction therefore contains particles which are defined by their enzyme content as lysosomes.5. Highly purified chromaffin granules, containing less than 5% of the activity of each acid hydrolase, were obtained from the gradient.