Vitamin K Dependent Modifications of Glutamic Acid Residues in Prothrombin

Abstract

A tetrapeptide, residues 6 to 9 in normal prothrombin, was isolated from the NH2-terminal, Ca2+-binding part of normal prothrombin. The electrophoretic mobility of the peptide was too high to be explained entirely by its amino-acid composition. According to 1H nuclear magnetic resonance spectroscopy and mass spectrometry, the peptide contained two residues of modified glutamic acid, -y-carboxyglutamic acid (3-amino-1,1,3-propanetricarboxylic acid), a hitherto unidentified amino acid. This amino acid gives normal prothrombin the Ca2 +_ binding ability that is necessary for its activation. Observations indicate that abnormal prothrombin, induced by the vitamin K antagonist, dicoumarol, lacks these modified glutamic acid residues and that this is the reason why abnormal prothrombin does not bind Ca2+ and is nonfunctioning in blood coagulation.Prothrombin is a plasma glycoprotein that is activated during the process of blood coagulation to the proteolytic enzyme thrombin. The biosynthesis of prothrombin is vitamin K dependent, and deficiency of this vitamin or administration of the vitamin K antagonist, dicoumarol, gives rise to an abnormal prothrombin which does not function in blood coagulation (1-6). The activation of prothrombin in vivo requires the binding of Ca2+ (7); abnormal prothrombin does not bind Ca2+ (2, 8, 9). During the activation of normal prothrombin an NH2-terminal fragment (molecular weight approximately 25,000) is split off; the difference between abnormal and normal prothrombin has been localized to this part of the molecule. Evidence has been produced that the difference is due to the lack of certain prosthetic groups in abnormal prothrombin (10-13).In an endeavour to define the difference between normal and abnormal prothrombin, the NH2-terminal fragments from both proteins were isolated and degraded further. A heptapeptide from normal prothrombin (residues 4 to 10) and a corresponding heptapeptide from abnormal prothrombin were isolated by BrCN degradation and trypsin digestion. The heptapeptide from normal prothrombin differed from the corresponding peptide in abnormal prothrombin in that it had a higher anodal electrophoretic mobility at pH 6.5 (13).By extensive proteolytic digestion, the heptapeptide from normal prothrombin was degraded to a tetrapeptide. This tetrapeptide, containing residues 6 to 9, still had an abnormally high anodal electrophoretic mobility at pH 6.5. This paper reports evidence that each of the two glutamic acid residues of this peptide are modified by replacement of one hydrogen on the -y carbon atom by a carboxyl group. This work will be described in greater detail elsewhere. MATERIALS AND METHODSIsolation of Tetrapeptide. The heptapeptide from normal prothrombin (residues 4 to 10) (ref. 13) was first thoroughly digested with aminopeptidase M (Sigma) and afterwards with carboxypeptidase B (Sigma). A tetrapeptide was isolated from the digest by gel chromatography on Sephadex G-25 superfine and obtained in pure form as judged by high voltage electrophoresis at...

The First γ-Carboxyglutamic Acid-containing Contryphan

“…Amino Acid Analysis and Sequencing-The amino acid composition of glacontryphan-M was determined after acid hydrolysis, except for Gla, which was measured after alkaline hydrolysis (40,41). For peptide sequencing a PerkinElmer Life Sciences (Foster City, CA) ABI Procise 494 sequencer was used according to the protocol from the manufacturer.…”

Vitamin K-dependent synthesis and modification of precursor prothrombin in cultured H-35 hepatoma cells.

“…During the past several years, much attention has been focused on the possibility that the inactive "abnormal" prothrombins (11)(12)(13) present in animals deficient in vitamin K or receiving coumarin anticoagulants may represent an unmodified species of mature prothrombin, i.e., precursor prothrombin. Evidence to support this view includes the presence and absence of y-carboxyglutamate residues in prothrombin and preprothrombin, respectively (14)(15)(16), the ability of inactive prothrombin to be converted to thrombin by Echis carinatus venom (8,17), the in vitro conversion of preprothrombin to prothrombin by rat liver microsomes (18), and the vitamin K-dependent incorporation of 14CO2 into prothrombin from liver microsomes of vitamin K-deficient rats (10).…”

Prothrombotic phenotype of protein Z deficiency

“…␥-Carboxyglutamic acid-mediated calcium ion binding in these proteins is necessary for their association with phospholipid surfaces and is critical for their hemostatic function (1,2). Prothrombin and factors VII, IX, and X are involved in the coagulant response leading to the generation of thrombin at sites of injury, whereas PC and PS play roles in an antithrombotic pathway that limits coagulation by inactivating the important coagulation cofactors Va and VIIIa (3).…”