Vitamin K-dependent carboxylation of blood coagulation proteins

Platelets and coagulation

Hemostasis is a multiple-component system. In order to function properly it has become highly integrated with several strategies of control. Failure of the system or its control can result in life-threatening hemorrhage requiring transfusion. It is hoped that the information provided in this article has enhanced the reader's understanding of hemostasis in animals, and will enable the reader to make a more educated choice concerning transfusion therapy for the bleeding patient.

Self-assembly of simian virus 40 large T antigen oligomers by divalent cations

In simian virus 40-transformed cells, simian virus 40 large T antigen can be detected in different forms separable by sucrose density gradient centrifugation. In our experiments, light forms sedimented around 5 to 7S, oligomers such as tetramers were detected around 16S, and higher aggregates sedimented in a broad distribution reaching above 23S. The oligomers sedimenting at and above 16S could be disassembled into the slowly sedimenting 5 to 7S forms by chelating agents [EDTA or ethylene bis(oxonitrilo)tetraacetate]. After the addition of divalent cations (CaCl2 or MgCl2) in excess of chelating agents, oligomeric forms reassembled and appeared in a sedimentation pattern resembling that observed before treatment with chelating agents. Time course studies permitted the identification of the 5 to 7S forms as precursors upon pulse-labeling (15 min); the 16S and higher oligomers were identified as the successors after a 14-h chase. Treatment of extracts of pulse-chase-labeled cells with chelating agents again disassembled the oligomers, whereas pulse-labeled precursors did not change their 5 to 7S sedimentation pattern. Adding an excess of divalent cations reassembled the pulse-chase-labeled T antigen to oligomers but did not influence the sedimentation behavior of pulse-labeled 5 to 7S precursors. It is therefore reasonable to assume that a posttranslational modulation induces divalent cation binding, leading finally to the oligomerization of T antigen. Thus, some of the multifunctional activities of T antigen can be dictated by divalent cation binding properties.

New method for the rapid detection of vitamin k deficiency

A new method is introduced for the rapid detection of vitamin K deficiency. The method is based on the direct measurement of the precursor factor II molecules that enter the blood in cases of vitamin K deficiency. The practical use of the new method has been evaluated on the basis of the results obtained in 28 plasma samples of patients suspected of liver disease and/or vitamin K deficiency.