[Factor X].

In 17 preterm neonates and 7 small-for-date neonates, all formula-fed, vitamin K-dependent coagulation factors II and X remained near 45% of adult values from the moment of birth until 28 days postnatally. Vitamin K1 levels, however, showed a remarkable rise from below the detection limit of 0.022 ng/ml in umbilical cord blood, to serum levels with a range of 0.99-7.29 ng/ml vitamin K1 on day 3, with a further rise on days 7 and 28 postnatally. Vitamin K1 (Konakion) parenterally given to a third group of four preterm neonates as a 1 mg dose resulted in very high serum levels of vitamin K1 (64.08-157.10 ng/ml), but without any significant increase in plasma levels of vitamin K-dependent coagulation factors II and X, compared to the group without any extra vitamin K1. It is concluded that in healthy preterm and small-for-date neonates no correlation is seen between serum levels of vitamin K1 and plasma levels of coagulation factors II and X. After administration of 1 mg Konakion no accelerated increase is seen in coagulation factor activities.

Factor X↗

PubMed1989

A new model to describe extrinsic protein binding to phospholipid membranes of varying composition: application to human coagulation proteins.

We introduce here a new model to describe the binding of extrinsic membrane proteins to acidic lipid membranes. In this view, macroscopic binding affinity is determined by two processes: nonspecific adsorption of protein to the membrane surface and association of acidic lipids with specific sites on the bound protein. We apply this model here to compare the binding of human prothrombin and factor X/Xa to phosphatidylglycerol (PG)- and phosphatidylserine (PS)-containing small unilamellar vesicles measured via relative light scattering. This comparison was undertaken because model membranes containing PS are much more effective in supporting thrombin formation than are membranes containing PG. Analysis of binding isotherms in terms of a traditional membrane binding model gave apparent dissociation constants systematically varying from 0.1 to 10 microM over a range of 8-65 mol% negatively charged phospholipid. With our new description of membrane binding, the dependence of binding data on the acidic lipid surface concentration revealed that only two or three acidic lipid molecules were associated with each surface-bound factor X/Xa or prothrombin molecule. Assuming four independent and equivalent acidic lipid binding sites per protein, it was possible to adjust the values of only the nonspecific adsorption equilibrium constant and the equilibrium constant describing binding of each species of acidic lipid to individual sites on the protein and thereby obtain a good simulation of log-linear binding isotherms for the full range of acidic lipid surface concentrations. The protein-associated binding sites had a greater affinity for PS than for PG; i.e., a lower surface concentration of PS was required to fill the binding sites.(ABSTRACT TRUNCATED AT 250 WORDS)

Factor X↗