Vitamin K, prothrombin, and gamma-carboxyglutamic acid

Quantitative adsorption of platelet glycoprotein G (thrombin-sensitive protein, thrombospondin) to barium citrate

Glycoprotein G (thrombin-sensitive protein, thrombospondin) is a high-Mr calcium-sensitive protein secreted by activated platelets. We observed that this protein was precipitated with barium citrate, and this property was used to purify glycoprotein G. The simple and rapid purification procedure consisted of barium citrate adsorption followed by heparin-agarose affinity chromatography. Unlike other calcium-sensitive proteins that are precipitated by barium citrate, glycoprotein G does not contain gamma-carboxyglutamic acid. The ability of glycoprotein G to bind to both heparin and barium citrate is consistent with this protein possessing clusters of positive and negative charges.

Monoclonal immunoglobulin M lambda coagulation inhibitor with phospholipid specificity. Mechanism of a lupus anticoagulant

Prolongation of all phospholipid-dependent coagulation tests was found in a patient with macroglobulinemia, despite absence of bleeding manifestations. The purified monoclonal IgM lambda protein and its Fabmu tryptic fragment induced similar changes in normal plasma. Patient IgM and Fabmu completely inhibited Ca++-dependent binding of radiolabeled prothrombin and Factor X to mixed phospholipid micelles. The patient's IgM lambda paraprotein reacted with phosphatidylserine and, to a lesser extent, with phosphatidylinositol and phosphatidic acid, but not with phosphatidylcholine or phosphatidylethanolamine. Prior incubation of phospholipid with patient Fabmu blocked the positive reactions. Substitution of washed platelets for phospholipid led to normalization of patient coagulation tests and corrected all abnormalities produced in normal plasma by patient IgM. Furthermore, binding of 125I-Factor Xa to thrombin-treated platelets was entirely normal in the presence of patient IgM. These studies support the concept that platelets, rather than phospholipid micelles, are the primary locus of prothrombin and Factor X activation in normal hemostasis.

Multiple aldehyde reductases of human brain

Human brain contains four forms of aldehyde reducing enzymes. One major activity, designated AR3, has properties indicating its identity with the NADPH-dependent aldehyde reductase, EC 1.1.1.2. The other major form of human brain enzyme, AR1, which is also NADPH-dependent, reduces both aldehyde and ketone-containing substrates, including vitamin K3 (menadione) and daunorubicin, a cancer chemotherapeutic agent. This enzyme is very sensitive to inhibition by the flavonoids quercitrin and quercetine, and may be analogous to a daunorubicin reductase previously described in liver of other species. One minor form of human brain aldehyde reductase, AR2, demonstrates substrate specificity and inhibitor sensitivity which suggest its similarity to aldose reductases found in lens and other tissues of many species. This enzyme, which can also use NADH as cofactor to some extent, is the most active in reducing the aldehyde derivatives of the biogenic amines. The fourth human brain enzyme ("SSA reductase") differs from the other forms in its ability to use NADH as well as or better than NADPH as cofactor, and in its molecular weight, which is nearly twice that of the other forms. It is quite specific for succinic semialdehyde (SSA) as substrate, and was found to be significantly inhibited only by quercetine and quercitrin. AR3 can also reduce SSA, and both enzymes may contribute to the production of gamma-hydroxybutyric acid in vivo. These results indicate that the human brain aldehyde reductases can play relatively specific physiologic roles.