LYSOSOMES, A NEW GROUP OF CYTOPLASMIC PARTICLES I5I 



optimum of the lysosomal cathepsin, this enzyme may be expected to become 

 active only below pH 6; i.e., below the norinal intracellular pH of liver (i8). 

 The peculiar type of release studied on liver slices (at pH 7.4) may thus apply to 

 a process occurring at a relatively high pH, while catheptic proteolysis may be- 

 come dominant in cells or cell regions exposed to acidification, as will be further 

 stressed below. It has indeed been found by Korner and Tarvcr (54) that the re- 

 lease of amino acids from isolated fractions is much increased by a lowering ot 

 the pH. 



Pathological Autolysis, Necrosis. Whatever may be the true physiological func- 

 tion of lysosomes, it is a fairly straightforward inference from the concept that 

 we have of these particles that an excessive release of their enzymes within the 

 cell may be associated with necrotic phenomena. As shown in figure i, the lyso- 

 somal enzymes are capable of destroying the most important tissue constituents, 

 and the principal defense of the cell against this attack may be assumed to lie in 

 the integrity of the lysosomal membrane. In surveying the older literature on 

 necrosis (see for instance the review by Bradley, 17), one is struck by the fact that 

 enzymes such as cathepsin ha\e long been suspected of playing a role in this 

 phenomenon, but no satisfactory explanation has been provided for their inhibi- 

 tion in the healthy cell. 



In our laboratory, the above hypothesis has been put to an experimental test 

 in collaboration with Dr. Beaufay and with a group of workers from the Cancer 

 Institute. In a first series of experiments, the results of which have so far been 

 published only in abstract form (8), a ligature was put on the vascular pedicle of 

 the left liver lobe of rats anesthetized with Nembutal. The animals were killed at 

 times ranging between one-half hour and 48 hours after the operation; the ligated 

 lobe and the healthy non-ligated part of the liver were taken out, homogenized 

 by a carefully standardized procedure, and centrifuged at high-speed. Enzyme 

 assays were performed on the whole homogenates, the sediments and the super- 

 natants. Some free activities were also measured on the whole homogenates. 



In figure 11 are shown the results relating to the cytochrome oxidase, glucose- 

 6-phosphatase and total acid phosphatase activities of the ligated lobes, expressed 

 in percentage of their activities in the non-ligated parts, which served as controls. 

 The rapid inactivation of the first two enzymes contrasts with the relative sta- 

 bility of acid phosphatase. The other lysosomal enzymes showed a more complex 

 behavior. The acid nucleases and cathepsin exhibited a progressive decrease to 

 about half the control values during the first 6-8 hours and then remained ap- 

 proximately constant; /^^-glucuronidase was unchanged for 6 hours and subse- 

 quently increased slowly. Of considerable interest were the changes in non-sedi- 

 mentable activities of lysosomal enzymes, which rapidly increased from an initial 

 mean value of 7 per cent of the total activities to a plateau of about 40 per cent. 

 This value was reached as early as 2-3 hours after ligation; thus at a time when. 



