Some properties of neutral-acting proteases and other degradative enzymes in rat leucocytes

Granules from rat liver cells and peritoneal leucocytes were shown to contain a protease which attacks haemoglobin, a ‘trypsin-like’ enzyme, elastase, ribonuclease, muramidase and phospholipase. Most of these enzymes from either source had two pH optima, one between pH 3.5 and 5.5, and another near neutrality (pH 6.5 to 7.5). Exceptions were the liver protease which was not active at neutrality, and elastase and muramidase which were not active at acid pH. When the leucocytes were disrupted with Triton X-1oo over 85 per cent of protease, phospholipase and elastase active at near-neutral pH remained membrane-bound and sedimentable, whereas about half of the phospholipase active at pH 4 and phosphatase active at pH 5 and pH 10 were released. Most of the β-glucuronidase and all of the acid protease were found in the supernatant. Differential and isopycnic centrifugation of leucocyte granules showed that the protease active at pH 8 was associated mainly with granules heavier and denser than those associated with protease active at pH 4. Acid and alkaline phosphatases were associated with the lighter granules.