Académie royale de Médecine de Belgique

|

Résumé Santiago Grisolia, correspondant étranger

(Séance du 18 juillet 1987)  

GOLGI APPARATUS, PUSH-PULL, PHOSPHORYL SUBSTRATE PROTECTOR AND CELL HETEROGENEITY, NEW PARAMETERS IN INTRACELLULAR PROTEIN TURNOVER

par Santiago GRISOLIA (Valence), correspondant étranger.

In spite on much work we are still in the dark regarding the extent, mechanism(s) and regulation of intracellular protein turnover.  We have recently commenced in our laboratory several approaches as well as continuing with more standard ones as follows :

1. Concerning interrelationships between protein synthesis and degradation, we have outlined a simple procedure consisting of incubating labeled mitochondria with cytosolic precursors of specific mitochondrial proteins and then measuring the release of proteins from mitochondria.  Since this procedure requires significant amounts of mitochondrial protein precursors, we are cloning cDNA of such important mitochondrial proteins as carbamoylphosphate synthase, ornithine transcarbamoylase and glutamate dehydrogenase in order to obtain specific mRNAs for “in vitro” translation.  Results obtained using apocytochrome c (precursor of cytochrome c) strongly suggest that mitochondrial protein turnover is regulated at the level of synthesis.

2. Low molecular weight phosphoryl compounds, such as 2, 3-diphosphoglycerate from proteolytic inactivation by proteases (rat liver lysosomal extracts, pronase, elastase).       

3. Immunogold procedures at the electron microscopic level using polyclonal and monoclonal antibodies for mitochondrial enzymes (carbamoylphosphate synthase, ornithine transcarbamoylase and glutamate dehydrogenase) show intercellular hetero-geneity in rat liver suggesting a preferential degradation of these proteins by the autophagic-lysosomal system.

4. Interestingly, degradation of short-lived proteins occurs by other mechanisms.  Centrifugation of cells grown in monolayer attached to the culture flasks, results in disorganization of the Golgi apparatus together with inhibition of the degradation of short-lived proteins, but not of long-lived proteins.  This suggest that this organelle partakes in the degradation of these proteins, by controlling the traffic of proteins or proteases to the degradation site(s).