Altered isoelectric focusing of alpha 2-macroglobulin from plasma of patients with diabetes mellitus.
Plasma from both type I and type II patients with diabetes mellitus displayed elevated alpha 2-macroglobulin trypsin-binding activity relative to normals. Column isoelectric focusing indicated that the average isoelectric point (pI) of the major form of crude alpha 2-macroglobulin was 6.6, 5.9, and 6.2 for normal, type I and type II subjects, respectively. Focused crude diabetic alpha 2-macroglobulin displayed significantly less recovered trypsin-binding activity relative to controls, particularly above a pI value of 6.0. Following preincubation with trypsin, the crude diabetic alpha 2-macroglobulin displayed a single isoelectric form (pI value of 5.3-5.5) and a substantial increase in recovered activity which were both comparable to normal alpha 2-macroglobulin. Purified alpha 2-macroglobulin from both normal and diabetic subjects displayed similar focusing profiles having a distribution of three forms with a pI value of 5.3-5.4 for the principal form. Trypsin-preincubated samples of purified alpha 2-macroglobulin displayed a single form with a pI value of 5.5-6.0. Preincubation of purified normal or diabetic alpha 2-macroglobulin with a plasma preparation devoid of alpha 2-macroglobulin from normal or diabetic plasma resulted in significantly lowered recovery of activity. All of the above studies suggest that the altered focusing properties observed for crude diabetic alpha 2-macroglobulin are due to components of the plasma rather than to alpha 2-macroglobulin itself.
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S A
SA
Lorenzi
M
M
Alhadeff
J A
JA
D000328:Adult; D000368:Aged; D003922:Diabetes Mellitus, Type 1 / Q000097:blood*; D003924:Diabetes Mellitus, Type 2 / Q000097:blood*; D006801:Humans; D007525:Isoelectric Focusing; D007526:Isoelectric Point; D008875:Middle Aged; D014357:Trypsin / Q000378:metabolism; D000511:alpha-Macroglobulins / Q000302:isolation & purification / Q000378:metabolism*
D000511:alpha-Macroglobulins; D014357:Trypsin