carboxypeptidase-b and Myocardial-Infarction

Isoforms of creatine kinase (creatine-N-phosphotransferase, CK, EC 2.7.3.2), BB and MB, were isolated from healthy human brain tissue and cardiac muscle, respectively, and were characterized by means of isoelectric focusing (IEF). CK-BB isoforms in Tris-HCl buffer were focused at pI 4.5 (a tissue form) and those in fresh sera from healthy adults were focused at pI 5.0, 5.1 and 5.2 (plasma forms). The IEF patterns of CK-BB isoforms were not altered following treatment with carboxypeptidase B and incubation in fresh serum at 37 degrees C; thus, it was found that there was no lysine at the C-terminal of the CK-B subunit and CK-BB isoforms were not results of the removal of lysine. Three CK-BB isoforms in fresh sera were identified to be oxidized, intermediate and reduced forms from the anodal side, respectively, by treatment with hydrogen peroxide and 2-mercaptoethanol. The oxidized form of CK-BB seemed to have higher affinity to IgG than the other two plasma forms of CK-BB. On the other hand, CK-MB isoforms in Tris-HCl buffer were focused at pI 5.4 (a tissue form) with a minor band at pI 5.2 and those in sera were focused at pI 5.0, 5.1, 5.2 (plasma forms) and 5.4. Four CK-MB isoforms were identified to be reduced, intermediate and oxidized forms without lysine from the anodal side, respectively, and the cathodal band was a tissue form with lysine.

Topics: Brain Chemistry; Carboxypeptidase B; Carboxypeptidases; Creatine Kinase; Humans; Isoelectric Focusing; Isoenzymes; Myocardial Infarction; Myocardium; Oxidation-Reduction

Human myocardial creatine kinase isoenzyme MM is present as a single form in tissue, but upon its release into plasma two additional forms, with faster anodal migration, are apparent on polyacrylamide electrophoresis. We designate the three forms as MM3, MM2, and MM1 in increasing order of anodal mobility. When tissue creatine kinase isoenzyme MM (MM3) is incubated with either carboxypeptidase N or carboxypeptidase B it is converted into the two additional forms, MM2 and MM1. The carboxy terminal amino acid of human, canine, and rabbit tissue MM3 was determined to be lysine, a specific substrate for carboxypeptidases N and B. Evidently the mechanism for the production of multiple forms of creatine MM in human plasma is the hydrolysis of a positively charged C-terminal lysine residue from one M subunit (MM2), followed by hydrolysis of the C-terminal lysine from the other subunit (MM1).

Topics: Animals; Carboxypeptidase B; Carboxypeptidases; Creatine Kinase; Dogs; Electrophoresis, Polyacrylamide Gel; Humans; Hydrolysis; Isoenzymes; Lysine; Lysine Carboxypeptidase; Myocardial Infarction; Rabbits