The isolation of purified neurosecretory granules from bovine pituitary posterior lobes. Comparison of granule protein constituents with those of neurophysin.

1. A procedure for the isolation of highly purified neurosecretory granules from the posterior lobe of the bovine pituitary gland is described. The preparation was free from contamination by the mitochondrial enzyme succinate dehydrogenase and the lysosomal enzyme cathepsin. 2. The biological activities of the neurosecretory granules were measured: the oxytocic activity was 11.61+/-1.30units and the pressor activity was 10.73+/-1.74units/mg. of protein. 3. A lysate of the isolated granules was shown to contain two proteins that appear to be identical with two of the constituents of neurophysin. 4. The constituents of neurophysin not present in neurosecretory granules could not be detected in any other subcellular fraction. It is suggested that the components of neurophysin not present in the neurosecretory granules arise as a result of the degradation of the two granular proteins.