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Murinoglobulin, a novel protease inhibitor from murine plasma. Isolation, characterization, and comparison with
Abstract:
Two glycoproteins having trypsin-protein esterase activity were purified to apparent homogeneity from murine plasma. One was alpha-macroglobulin, a homologue of human alpha-2-macroglobulin, while the other, tentatively named murinoglobulin, did not correspond to any of the known plasma protease inhibitors that have been well characterized in men or other mammals. Murinoglobulin contained about 7.6% carbohydrate and was composed of a single-polypeptide chain of Mr = 180,000 as judged by the equilibrium sedimentation analysis and sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing conditions. Murinoglobulin did not cross-react immunologically with mouse alpha-macroglobulin nor with human alpha-2-macroglobulin. Protease-inhibiting properties of murinoglobulin were compared with those of mouse alpha-macroglobulin and human alpha-2-macroglobulin. All the three proteins inhibited trypsin, papain, and thermolysin, although they differed considerably in both the degree of inhibition and the binding stoichiometry of protease-inhibitor complexes. The two macroglobulins inhibited pepsin at pH 5.5, whereas murinoglobulin was inactivated at this pH. Murinoglobulin was more sensitive to methylamine than the two macroglobulins. No protein corresponding to murinoglobulin was detected in human plasma.
Insights
Researchers purified two plasma glycoproteins with trypsin-protein esterase activity from mice. One is alpha-macroglobulin; the other, murinoglobulin, is a novel protease inhibitor distinct from known mammalian inhibitors.
Area of Science:
- Biochemistry
- Proteomics
- Immunology
Background:
- Plasma contains various glycoproteins with protease inhibitory functions.
- Alpha-macroglobulins are key plasma protease inhibitors found across species.
- Characterization of novel plasma proteins is crucial for understanding biological systems.
Purpose of the Study:
- To purify and characterize novel glycoproteins with trypsin-protein esterase activity from murine plasma.
- To compare the properties of a newly identified protein, murinoglobulin, with known alpha-macroglobulins.
Main Methods:
- Purification of glycoproteins from murine plasma using standard biochemical techniques.
- Characterization of purified proteins using equilibrium sedimentation and SDS-PAGE.
- Immunological cross-reactivity assays and comparison of protease inhibition profiles.
Main Results:
- Two glycoproteins were purified: murine alpha-macroglobulin and a novel protein, murinoglobulin.
- Murinoglobulin is a single-chain glycoprotein (Mr = 180,000) lacking immunological cross-reactivity with known macroglobulins.
- Murinoglobulin exhibits distinct protease inhibition patterns compared to alpha-macroglobulins, including sensitivity to acidic pH and methylamine.
Conclusions:
- Murinoglobulin represents a novel class of plasma protease inhibitor in mice.
- Its unique biochemical and functional properties differentiate it from alpha-macroglobulins.
- The absence of a human homologue suggests species-specific evolution of plasma protease inhibitors.