Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:4.1.2.13 (aldolase)
 3,461 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The number of rat liver autophagic vacuoles (AVs) was increased by separate injection of three different inhibitors--vinblastine, leupeptin, and chloroquine--of lysosomal protein degradation. The different mechanisms of action of the agents correlated to the ultrastructure of the AVs. Accumulation of the base chloroquine with ensuing influx of water into AVs caused a significant swelling. The leupeptin-induced AVs were processed into residual-body-like structures within a few hours of exposure in line with the presence of a leupeptinase in liver tissue. Vinblastine was the most efficient agent in increasing the occurrence of AVs. The effect of vinblastine lasted for the entire study period (36 hr) with continuous formation of nascent AVs. In addition, vinblastine caused the appearance of a subpopulation of AVs laden with VLDL particles. The term crinosomes was suggested for these hybrid organelles, since they seemed to evolve by fusion between secretory granules and lysosomes. In addition to sequestered cell organelles, the AVs harbored cytosolic enzyme activities (LDH and aldolase). Leupeptin was the only agent that caused a decrease in cathepsin B and L activities. Similarly, leupeptin impeded protein breakdown in isolated AVs, whereas vinblastine and chloroquine evoked an increase. In vivo, chloroquine and vinblastine block protein degradation. The reason for this discrepancy is probably that during in vivo exposure the substrate (cytoplasmic proteins) is built up in the AVs because degradation is retarded. Upon isolation of the AVs the inhibitor block is released, and proteolysis proceeds at enhanced rates over control due to excess of substrates. Leupeptin, on the other hand, caused a substantial inhibition of thiol proteinases; this block remained in the isolated AVs. Accordingly, leupeptin-induced AVs displayed decreased protein degradation following shorter exposure times. Later, when leupeptin was metabolized, catch-up proteolysis was noted. The differing mechanisms of action of the inhibitors were also apparent as regards lipid contents and lipolysis. Whereas chloroquine and vinblastine increased the amounts of cholesterol and triglycerides parallel to proteins, leupeptin had no such effect. Lipolysis proceeded at normal rate following leupeptin administration, which was not the case after vinblastine and chloroquine exposure. Leupeptin has no effect on acid lipases; therefore lipids do not accumulate in AVs of hepatocytes that are exposed to leupeptin.
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PMID:Comparison of different autophagic vacuoles with regard to ultrastructure, enzymatic composition, and degradation capacity--formation of crinosomes. 367 66

Injection of leupeptin (an inhibitor of lysosomal cathepsins B, H, and L) to nonstarved rats causes an expansion of the autophagic vacuolar (AV) system in hepatocytes. Readily identifiable cytoplasmic constituents were seen within the AVs shortly after the administration. Later, the contents of the AVs seemed to reach more advanced stages of degradation. Liver AVs were purified by a one-step centrifugation of a crude mitochondrial lysosomal fraction in a discontinuous metrizamide gradient after exposing the rats to leupeptin for varying periods of time. Leupeptin caused alterations of the AV fraction that were time dependent. Initially, i.e., after 30 minutes of leupeptin exposure, mature (secondary) lysosomes clearly dominated over nascent AVs. The situation was reversed when fractionation was performed 1 or 2 hours following the injection of leupeptin. Now, the AVs were more frequent than the mature lysosomes. Later, the proportion of mature lysosomes was again larger. An increase in dense bodies was noted after 16 hours of leupeptin treatment. The proteolytic capacity of the AVs at different stages of maturation was measured after labeling liver proteins with an injection of L-1-14C-leucine 16 hours before sacrifice. AVs were purified after varying times of exposure to leupeptin. The proteolysis decreased greatly 1 to 2 hours following the injection of leupeptin but never ceased. On the other hand, lipolysis seemed unaffected by leupeptin using a similar experimental protocol as for proteolysis. If the animals were subjected to more lasting exposure to leupeptin before fractionation, proteolysis increased, displaying a peak higher than control, occurring after approximately 4 hours. The degradation gradually returned to control values after 16 hours. A catch-up in proteolysis was thus observed. The time course of proteolysis was reflected in the protein content in the AV fraction. After an initial increase that coincided with the lowered proteolysis, it returned to control level. Marker enzyme activities for endoplasmic reticulum and mitochondria (G6Pase and succinate-cytochrome c reductase) followed the same pattern. The AV content of the cytosolic enzymes lactate dehydrogenase and aldolase reached as high as 2.30 and 2.80% of the values in the homogenate during the 1st hour of leupeptin exposure. From these data the half-lives of the enzymes were calculated. They were: for aldolase, 43 hours; for LDH, 68 hours. This suggests that AVs account for a substantial proportion of degradation not only of organelles but also of soluble cytosolic enzymes.
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PMID:Effect of leupeptin on the autophagic vacuolar system of rat hepatocytes. Correlation between ultrastructure and degradation of membrane and cytosolic proteins. 633 Apr 53