Hepatic tissue has two pathways for phosphatidylcholine (PC) synthesis, i.e., the cytidinediphosphocholine (CDP-choline) pathway and the methylation pathway, which utilizes phosphatidylethanolamine-N-methyltransferase (PEMT). Fatal liver damage occurs in Pemt(-/-)mice fed a choline-deficient (CD) diet. We investigated whether liver damage can be reversed by the addition of dietary choline. Mice (8 wk old) were fed the CD purified diet for 4 d, a choline-supplemented (CS) diet (CD diet + 0.4% choline chloride) for 4 d, or the CD diet for 3 d and a CS diet for 1 d (CD/CS). Pemt(-/-)mice fed the CD diet for 3 d exhibited liver damage as assayed by plasma aminotransferase levels. The livers appeared normal after subsequent feeding of the CS diet for 1 d (CD/CS). The activities of plasma aminotransferases of CD/CS fed mice were comparable to Pemt(-/-)mice fed the CS diet. Hepatic PC and triacylglycerol levels as well as plasma PC levels in the CD/CS-fed Pemt(-/-)mice were lower than those of mice fed the CD diet and began to approach normal levels. Although the CD diet induces liver damage in Pemt(-/-)mice, this damage can be rapidly reversed by the addition of dietary choline.

The adsorption behavior of holo- and apo-α-lactalbumin at a Pt/electrolyte interface was studied in an acidic, neutral, and alkaline medium over the temperature range 273 to 353 K, using the cyclic voltammetry technique. It was shown that the surface charge density, resulting from protein adsorption, is directly proportional to the amount of adsorbed protein (surface concentration), indicating that adsorption is accompanied by the transfer of charge. A significant difference in the amount of adsorbed protein (between the two types of protein) was obtained at pH 7 because of the difference in conformation of the molecule in the presence/absence of bound calcium. On the other hand, the resemblance in behavior of the two types of proteins observed at pH 2 and pH 11 suggested that the protein is in its molten globule state and is depleted in calcium at these pHs. The adsorption process was modeled using the Langmuir adsorption isotherm. The values of the Gibbs free energy of adsorption indicated that the protein molecules strongly adsorb onto the Pt surface via chemisorption. The protein expressed the highest affinity toward adsorption at pH 2 and the lowest at pH 11. The adsorption process was found to be endothermic, resulting from the excess energetics required for the breaking of intramolecular interactions relative to those involved in the formation of protein−metal bonds. The adsorption of α-LA onto a Pt surface was found to be an entropically governed process, suggesting structural unfolding of the protein at the electrode surface.

No abstract