Hydrolysis of succinyl-trialanine p-nitroanilide by two enzymes associated with human high-density lipoproteins

Early modifications of outgrowth and metallo-endopeptidase activity in fibroblasts from rat cutaneous explants after local gamma-irradiation: dermis cellularity and collagen fibre alterations

The initial response to local gamma-irradiation of skin was investigated in fibroblasts from cutaneous explants after doses of 4, 8, 12, 16 or 20 Gy. On the day of irradiation, fibroblast outgrowth was inhibited in a dose-dependent manner, but by day 7 post-irradiation, cell restoration occurred especially in explants exposed to 4 or 8 Gy. The dose-dependent inhibition of fibroblast outgrowth correlated with the decrease in cellular metallo-endopeptidase (MEP) activity against succinyl trialanine paranitroanilide. However, the secretion of this MEP activity was 10-fold higher in the culture medium after the lowest irradiation dose (4 Gy). Its inhibition profile was not modified after local irradiation, whatever the dose. In vivo, the cell density of mastocytes, pericytes and endothelial cells decreased after irradiation. Moreover, damaged collagen was observed in the superficial dermis after local irradiation. These results strongly suggest that this MEP may be involved in the alterations occurring in dermal connective tissue components after skin irradiation. The rapid decrease with the dose in fibroblast outgrowth and MEP activity also suggests that these two parameters may provide useful tools for dosimetric assay of the heterogeneity and extent of irradiated areas.

Pre-beta high density lipoprotein. Unique disposition of apolipoprotein A-I increases susceptibility to proteolysis

Apolipoprotein A-I-containing lipoproteins (high density lipoproteins, HDL) can be separated into two subfractions, which have pre-beta and alpha electrophoretic mobilities, respectively. These fractions differ in both composition and structure. Some preparations of pre-beta-migrating HDL, but not alpha-migrating HDL, were found to contain two polypeptides with Mr of approximately 26 and 14 kDa, which are scission products of apolipoprotein (apo) A-I. They are recognized by monospecific antibodies to apo A-I and have N-terminal sequences identical to those of mature apo A-I. This proteolytic scission of apo A-I occurs primarily after venipuncture. Immediate addition of protease inhibitors minimized the appearance of the fragments in plasma. To study the relative susceptibilities of pre-beta and alpha HDL to proteolysis, the lipoproteins were incubated in vitro with plasmin. The apo A-I in pre-beta HDL was extensively degraded, but that in alpha-migrating HDL was degraded to a much lesser extent, indicating that the appearance of apo A-I fragments in pre-beta HDL was due to enhanced sensitivity to proteolysis. To varying degrees, thrombin, kallikrein, elastase, arginine C endoprotease, and chymotrypsin also appear to cleave pre-beta HDL faster than alpha HDL. Most of the proteases generated a 12 to 14 kDa peptide fragment under conditions of limited cleavage. These results suggest that the conformational state of apo A-I in pre-beta-migrating HDL or its spatial relationship to lipids is significantly different from that of apo A-I in alpha-migrating HDL.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of human skin fibroblasts elastase activity

We present evidence that enzyme activity hydrolyzing Succinoyl trialanine paranitroanilide (Suc(Ala)3NA) expressed by Human Skin Fibroblasts (HSF) in culture could be attributed to the concerted action of an endopeptidase and an aminopeptidase(s). Both endopeptidase and aminopeptidase activities were strongly inhibited by metal chelating agents and Copper and Zinc ions but were insensitive to Tissue Inhibitor of Metallo Proteases (TIMP). These protease activities coeluted on ion exchange chromatography (DEAE Tris acryl M) and were further separated by high-performance liquid chromatography HPLC (TSK 3000 SW). The endopeptidase activity, designated as HSF E1, was eluted at the position corresponding to an Mr equal to 94,000. It has only a limited elastinolytic potential as evaluated on 3H insoluble elastin, but it extensively degrades human skin elastic fibers as directly assessed on human skin tissue sections and further quantitated by automated image analysis. The level of HSF E1 increases with the number of fibroblast passages.

A simple and sensitive chromogen assay for the measurement of elastase-type enzyme activity in human plasma

A highly sensitive, precise and fast automatic chromogen assay has been developed for estimation of elastase-type activity in plasma using 3-carboxypropionyl-trialanine p-nitro-anilide as substrate. The assay is linear up to at least 8.7 U/l and has a detection limit of 0.003 U/l. The study demonstrates that this enzyme activity is due to one or several metalloproteinases with pH optimum at physiological pH. The plasma enzyme activity in 37 healthy persons ranged from 0.10 U/l to 0.63 U/l. The individual day to day variation was found to be about 12%. In plasma pools prepared from randomly taken samples of in- and out-patients the activity was found up to 8.7 U/l. The origin of the metalloelastase activity is discussed.

Proteolytic processing and compartmentalization of the primary translation products of mammalian apolipoprotein mRNAs

The steps involved in the initial assembly of apolipoproteins and lipids into supramolecular arrays (nascent lipoprotein particles) are largely unknown. Examination of the proteolytic processing and compartmentalization of the primary translation products of apolipoprotein mRNAs represents one approach to deciphering the molecular details of lipoprotein assembly. The structures of the primary translation products of seven mammalian apolipoprotein mRNAs has been determined in the past several years. The organization of apolipoprotein signal peptides is typical of eukaryotic prepeptides, although an unusual degree of sequence conservation is present among the signal segments of apo AI, AIV, and E. For those apolipoprotein sequences studied in detail, SRP-dependent cotranslational translocation and proteolytic processing appears to be highly efficient and results in sequestration of the processed protein within the lumen of the endoplasmic reticulum (ER). However the mechanism by which these lipid-binding proteins avoid arrest during their translocation through the lipid bilayer of the ER membrane remains obscure. The two principal human HDL apolipoproteins undergo novel extracellular post-translational proteolytic processing, which results in removal of nonhomologous propeptides. The proteases responsible for proapo AI and AII processing appear to be different. The processing of these proapolipoproteins provides a potential series of steps for regulating the ordered assembly of HDL constituents.