A new blood-coagulating protease in mitochondrial membranes of rat submaxillary glands. Purification and characterization of protease and its blood-coagulating activity

Protein degradation in mitochondria: implications for oxidative stress, aging and disease: a novel etiological classification of mitochondrial proteolytic disorders

The mitochondrial genome encodes just a small number of subunits of the respiratory chain. All the other mitochondrial proteins are encoded in the nucleus and produced in the cytosol. Various enzymes participate in the activation and intramitochondrial transport of imported proteins. To finally take their place in the various mitochondrial compartments, the targeting signals of imported proteins have to be cleaved by mitochondrial processing peptidases. Mitochondria must also be able to eliminate peptides that are internally synthesized in excess, as well as those that are improperly assembled, and those with abnormal conformation caused by mutation or oxidative damage. Damaged mitochondrial proteins can be removed in two ways: either through lysosomal autophagy, that can account for at most 25-30% of the biochemically estimated rates of average mitochondrial catabolism; or through an intramitochondrial proteinolytic pathway. Mitochondrial proteases have been extensively studied in yeast, but evidence in recent years has demonstrated the existence of similar systems in mammalian cells, and has pointed to the possible importance of mitochondrial proteolytic enzymes in human diseases and ageing. A number of mitochondrial diseases have been identified whose mechanisms involve proteolytic dysfunction. Similar mechanisms probably play a role in diminished resistance to oxidative stress, and in the aging process. In this paper we review current knowledge of mammalian mitochondrial proteolysis, under normal conditions and in several disease states, and we propose an etiological classification of human diseases characterized by a decline or loss of function of mitochondrial proteolytic enzymes.

Epi p 1, an allergenic glycoprotein ofEpicoccum purpurascensis a serine protease

Epicoccum purpurascens (EP) is a ubiquitous saprophytic mould, the inhalant spores and mycelia of which are responsible for respiratory allergic disorders in 5-7% of population worldwide. The diagnosis/therapy of these disorders caused by fungi involves the use of standardized and purified fungal extracts. A 33.5 kDa glycoprotein, Epi p 1 released histamine from whole blood cells of EP allergic patients at a concentration of 50-ng protein. The high specific IgE values detected in EP hypersensitive sera indicated that Epi p 1 is capable of mediating type I hypersensitive reaction in predisposed individuals. It also showed protease activity by virtue of its dose dependent cleavage of serine protease specific synthetic substrate, N-benzoyl arginine ethyl ester hydrochloride (BAEE). The serine protease nature of Epi p 1 was confirmed by its N-terminal sequence (ADG/FIVAVELD/STY) homology to a subtilisin like serine protease. The protease activity of Epi p 1 may be responsible for making its way into the system of pre-disposed individuals through epithelial cell detachment and the histamine releasing ability by cross-linking of IgE antibodies on cell surface is the cause of its allergenic nature.

Protease activation during surgical stress in the rat small intestine

BACKGROUND

Surgical stress affects intestinal permeability and our earlier study using a rat model indicated that oxidative stress plays an important role in this process. Proteases are important mediators of cellular damage and are known to be activated in oxidative stress. This study looked at protease activity in enterocytes after surgical stress.

METHODS

Surgical stress was induced by opening the abdominal wall and handling the intestine as done during laparotomy, in normal and xanthine oxidase-deficient rats. Enterocytes at various stages of differentiation were isolated and protease activity and protection offered by xanthine oxidase inhibitors were determined. Mitochondria and cytosol were prepared from total isolated enterocytes at different periods after surgical stress and protease activation was studied.

RESULTS

Surgical stress induced activation of proteases in both the villus and crypt cells. Protease activation is seen in both mitochondria and cytosol, and similar to the other alterations in mucosal cells, protease activation was maximum 60 min after stress, returning to normal by 24 h. Thiol compounds modulate protease activity in both mitochondria and cytosol and the activation is not seen in xanthine oxidase-deficient animals.

CONCLUSIONS

Surgical stress induces activation of proteases in villus and crypt cells of the small intestine. Both mitochondrial and cytosolic proteases are activated and free radicals generated by xanthine oxidase may mediate protease activation after surgical stress in the intestine.