Synthesis of clotting factors by a cell-free system from rat liver in response to the addition of vitamin K1 in vitro

Post-translational carboxylation of preprothrombin

In summary, in this review on the function of vitamin K in post-translational modification of precursor proteins by carboxylation of certain glutamyl residues, I have tried to cover in particular the recent work on the reaction, the enzymes involved and the mechanisms being considered. In doing this I have also considered vitamin K, its discovery, its functional form and the possible relation of its metabolism to the carboxylation reaction. Equally the various vitamin K-dependent gla-containing proteins currently known have been described. The carboxylation of synthetic small molecule exogenous substrates and the synthesis and metabolism of the products of carboxylation are of great help in studying the reaction. Structural specificity of vitamin K analogs in vivo and in vitro has been compared and the use of various antagonists in vivo and in vitro considered in attempts to gain an understanding of the overall reaction. The reactions subsequent to carboxylation, e.g., the activation of prothrombin to thrombin via serine proteases and the related activation of the other vitamin K-dependent proteins have not been considered in this review. The review has not covered prothrombin or other vitamin K-dependent protein isolation, nor the determination of these proteins. As the vitamin K-dependent protein carboxylation story has developed over the past six years, a number of reviews have been written which help in keeping up with the various aspects of the field as it has expanded. These reviews refer to many of the papers I have had to eliminate due to space limitations. They are referenced as 469-489. The review is in no sense comprehensive and many papers have been missed or only mentioned. I have tried to concentrate on the more recent work and, thus, much of the very fine work of the 1940's on vitamin K chemistry is hardly mentioned. Some redundancy has been built into the organization of the review so that a reader can obtain a reasonable view of any one section without having to search the whole review for all possible relevant information on any particular part of the field.

Adaptation of the salmonella/mammalian microsome test to the determination of the mutagenic properties of mineral oils

Two techniques allowing the determination of the mutagenicity of lipophilic compounds such as mineral oils with the Ames test have been developed by using benzo[a]pyrene (BP) dissolved in white oil as a synthetic reference oil. The first technique involves prior extraction of polynuclear aromatic hydrocarbons (PAH) with dimethyl sulfoxide. In the second method, which proved simpler and of more general use, the compounds to be tested are directly dispersed in aqueous medium with Tween 80. The use of these techniques made possible the study of mutagenicity of various kinds of mineral oil. Mutagenic activity was found in used crankcase oils, and also in petroleum distillates but much less in solvent-refined oils. A good correlation was observed between mutagenic activity and PAH content but not BP content of oils. Because of their peculiar response to the test, petroleum distillates were studied in more detail. When added in low amounts to pure PAH compounds such as BP, they enhanced its mutagenic activity (enhancement). When added in higher amounts, on the contrary, these oils completely inhibited BP mutagenic activity (inhibition effect). Both effects correlated well with the PAH content and the mutagenic activity of the petroleum distillates tested. These results explain the abnormal dose-response curves curves obtained with these petroleum distillates and the negative results regarding their mutagenic activity reported in earlier studies. A likely explanation is discussed for the enhancement and inhibition effects.

Mechanism of action of vitamin K: synthesis of gamma-carboxyglutamic acid

Vitamin K (2-methyl-3-phytyl-1,4-naphthoquinone) is required for the synthesis of prothrombin, Factor VII, Factor IX, Factor X, and a number of newly discovered proteins. These plasma proteins participate in calcium-dependent phospholipid membrane interactions which are mediated through the presence of gamma-carboxyglutamyl residues in their amino-terminal region. Vitamin K is required for the postribosomal conversion of glutamyl residues in liver precursors of these proteins to gamma-carboxyglutamyl residues in the completed plasma proteins. In the absence of vitamin K, or in the presence of vitamin K antagonists, animals produce plasma forms which lack the carboxylated residue. These proteins are nonfunctional because of their lack of phospholipid interaction. The vitamin K-dependent carboxylase which carries out this reaction has been studied in rat liver microsomal preparations where it will carboxylate the endogenous precursor proteins. Low-molecular-weight glutamyl-containing peptide substrates, such as Phe-Leu-Glu-Glu-Leu, which are homologous to regions of the prothrombin precursor, will also serve as substrates for the detergent-solubilized enzyme. This enzyme has been shown to require the reduced form of the vitamin and O2 but no ATP or a biotin-containing protein for its activity. The same microsomal preparations will also convert vitamin K to its 2,3-epoxide, and it is possible that activity may be related to the role of the vitamin in driving the carboxylase reaction.

The effect of warfarin and vitamin K-1 on the carboxylation and glycosylation of prothrombin in vivo

The effect of warfarin and vitamin K-1 on the carboxylation and glycosylation of prothrombin in the rat in vivo was investigated. Neither warfarin nor vitamin K-1 had an effect on carboxylation. However, warfarin inhibited glycosylation 80-90% and this inhibition was readily reversed by the administration of vitamin K-1.

In vitro prothrombin synthesis from a purified precursor protein. II. Partial purification of bovine carboxylase

In this paper, we describe the isolation and partial purification of an enzyme system that converts bovine decarboxyfactor II (PIVKA-II) into prothrombin (factor II). It is shown that the increase in factor II activity occurs in parallel with 14CO2 incorporation into BaSO4 adsorbable proteins. The system is not strictly vitamin K-dependent because it is obtained from the livers of normal healthy cows. By preincubating the enzyme(s) with an excess of warfarin, an absolute vitamin K1-dependence can be obtained. The reaction is inhibited by its own product, factor II.