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Biomedical subjects

E Melloni

Publications and source records attributed to E Melloni.

At least 163 records · Page 9Linked to original sources
PubMed1984

Ca2+-dependent neutral proteinase from human erythrocytes: activation by Ca2+ ions and substrate and regulation by the endogenous inhibitor.

Ca2+-dependent neutral proteinase purifies from human erythrocytes as an inactive proenzyme, that can be converted in an active low Ca2+ requiring form either by high concentrations of Ca2+ (0.1-1 mM) in the absence of the substrate, or by low concentrations of Ca2+ (1-5 microM) in the presence of digestible substrates. Activation requires dissociation to constituent inactive proenzyme subunits which are then converted to the active proteinase species still retaining their monomeric structure. The activation process produced by high Ca2+ concentrations is controlled by the endogenous inhibitor which also dissociates into constituent subunits in order to exert its inhibitory effect. An additional regulation of the activated proteinase involves an autoproteolytic process, Ca2+ and substrate dependent, producing enzyme inactivation.

Calcium↗
PubMed1983

Effectiveness of laser photoradiation therapy following hematoporphyrin derivative administration in the experimental MS-2 tumor model.

The effectiveness of laser photoradiation therapy with hematoporphyrin derivative sensitization was tested in the MS-2 sarcoma. This solid tumor, transplanted into the pad of the hind leg of BALB/c mice, was found to be a sensitive experimental model for a quantitative evaluation of response to phototherapy and for determination of critical parameters in laser phototherapy treatment. Under our experimental conditions, optimal therapeutic effects appeared to be critically dependent on drug dose, number of treatments, light intensity, and irradiation of the peripheral border of the tumor.

Animals↗
PubMed1983

Endogenous inhibitors of lysosomal proteinases.

Specific inhibitors of three lysosomal proteinases are present in the cytosolic and lysosomal compartments of rabbit liver. The cytosolic inhibitors, purified by chromatography on DEAE-Trisacryl and Sephadex G-75, show specificities toward cathepsin M, cathepsins B and L, and fructose 1,6-bisphosphatase converting enzyme (CE), respectively, and are designated IM, IB/L, and ICE. Inhibitors with similar specificities have been isolated from the intralysosomal compartment. Two of these inhibitors, IM and ICE, are also present in the lysosomal membranes. The lysosomal distribution parallels that of the respective proteinases. The inhibitors are polypeptides with molecular weights of 5,000-10,000 for the two forms of IB/L, 12,500 for IM, and 10,000-40,000 for the ICE species.

Animals↗
PubMed1982

Characterization of the inactive form of fructose-1,6-bisphosphate aldolase isolated from livers of fasted rabbits.

The accumulation of an inactive, immunologically crossreactive form of fructose-1,6-bisphosphate aldolase (EC 3.1.3.11) in livers of fasted rabbits has now been related to limited proteolysis at the COOH terminus. The extent of modification of this region of the molecule, determined by analysis of tyrosine residues in the peptides released by digestion with subtilisin, agrees with the observed decrease in the specific activity of the enzyme purified from livers of fasted rabbits. The following evidence supports the conclusion that the modified form is produced in vivo and not during the isolation of the enzyme from the liver homogenates: (i) liver homogenates prepared in isotonic sucrose contained negligible amounts of soluble lysosomal proteinases; (ii) the decreased aldolase activity after fasting was observed in the homogenates and no change in aldolase activity occurred when the homogenates were incubated for 2 hr at 37 degrees C; (iii) the modified enzyme was also isolated from the livers of fasted rabbits when leupeptin was injected intraportally before the animals were sacrificed or when the inhibitor was added to the homogenization solution. On the other hand, homogenization of livers in hypotonic medium resulted in release of lysosomal proteinases and also in decreases in catalytic activity and COOH-terminal modification of liver aldolase, similar to those observed in livers from fasted rabbits. We attribute the changes in activity and structure of aldolase isolated from livers of fasted rabbits to the action in vivo of cathepsin M.

Animals↗
PubMed1982

Limited proteolysis of liver aldolase and fructose 1,6-bisphosphatase by lysosomal proteinases: effect on complex formation.

Cathepsin M, which catalyzes inactivation of both rabbit liver fructose-1,6-bisphosphate aldolase (EC 4.1.2.13) and rabbit liver fructose 1,6-bisphosphatase (Fru-P2ase; EC 3.1.3.11), has been characterized as a peptidyl peptidase. Modification of the COOH terminus of aldolase by cathepsin M or by Fru-P2ase converting enzyme 2 abolishes its ability to bind to phosphocellulose P11 and to form the complex with Fru-P2ase. On the other hand, modification of the COOH terminus of Fru-P2ase does not affect its interaction with aldolase. This property is lost, however, when Fru-P2ase is modified in the NH2-terminal region by the converting enzyme or by subtilisin. The results suggest that interaction of aldolase and Fru-P2ase may involve the exposed COOH-terminal region of the former and an exposed proteinase-sensitive region located between residues 57 and 67 of the latter.

Amino Acids↗
PubMed1981

Decay of proteinase and peptidase activities of human and rabbit erythrocytes during cellular aging.

Variations in activity of the membrane-bound and cytosolic proteinases and peptidases were analyzed in human and rabbit erythrocytes at various stages of their life-span. The patterns observed with human erythrocytes were the following. (a) The acidic endopeptidase activity associated with the membranes undergoes a substantial decline during cellular aging, with an estimated half-life of 65 days. Concomitantly it appears to become progressively more latent. (b) All cytosolic proteinase and peptidase activities described previously (Pontremoli, S., Melloni, E., Salamino, F., Sapartore, B., Michetti, M., Benatti, U., Morelli, A. and De Flora, A. (1980) Eur. J. Biochem. 110, 421-430) decline exponentially throughout the erythrocyte life-span, with the exception of dipeptidyl aminopeptidase III. The calculated half-lives were: 60 days for the neutral endopeptidase; 87 days for the total acidic endopeptidase activity which is accounted for by three distinct enzymes; 49 days for aminopeptidase B and 133 days for a second aminopeptidase with broad substrate specificity; 84 days for dipeptidyl aminopeptidase II. The results obtained with the rabbit erythrocytes were: (a) no significant decline of leucine aminopeptidase, dipeptidyl aminopeptidase II and III activities in the transition from reticulocytes to mature erythrocytes; (b) very limited decline of aminopeptidase B activity; (c) a pronounced age-dependent decay, in increasing order, of neutral endopeptidase, aminopeptidase A, carboxypeptidase and acidic endopeptidase activities.

Aminopeptidases↗