Some factors affecting enzyme release from cerebral lysosomes: inhibitory effects of lead.

The mode of the inhibitory effect of lead ion on the release of enzymes from cerebral lysosomes isolated from young Wistar rats was examined. The incubation of cerebral lysosomes in a low pH medium or with adenosine triphosphate (1 mM) at neutral pH resulted in the decrease of the release of acid phosphatase (EC 3.1.3.2) and beta-N-acetylglucosaminidase (EC 3.2.1.30) activities. Multivalent cations such as Mn2+, Co2+ and La3+ inhibited the enzyme release, while Ca2+ facilitated the release. On the other hand, lead ion suppressed the Ca2+-induced enzyme release, but this suppressive effect of lead ion was eliminated by the treatment of lysosomes with phospholipase C and phospholipase A2. These results suggest that lead ion may alter the ionic permeability of cerebral lysosomal membrane by reacting with membraneous phospholipids, and thus may prevent the release of lysosomal enzymes in vitro.