HUMAN PLASMA PHOSPHOLIPID TRANSFER PROTEIN ACCELERATES EXCHANGE TRANSFER OF ALPHA-TOCOPHEROL BETWEEN LIPOPROTEINS AND CELLS

alpha-Tocopherol (alpha-T), an important anti-oxidant of plasma lipopr oteins and cell membranes, is secreted from liver together with very-l ow-density lipoproteins into the blood stream. Other serum lipoprotein classes gain alpha-T by exchange and transfer processes. We show here that the lipoprotein-free d > 1.22 g/ml fraction of human or pig seru m increases the exchange rate. of alpha-T by a factor of 2-4 as compar ed with spontaneous exchange/transfer. The alpha-T exchange/transfer ( alpha-TET) activity was purified by multiple-step column chromatograph y. It gave a single band in PAGE with an apparent molecular mass of 75 kDa, and was found to be identical with the phospholipid transfer pro tein (PLTP). PLTP catalysed alpha-T exchange between different lipopro tein classes, as well as the transfer of alpha-T from artificial lipos omes to high-density lipoproteins. The alpha-TET activity measured wit h a newly developed assay in ten healthy people was 2.45+/-0.88 nmol.m l(-1).h(-1). alpha-TET activity was negatively correlated with plasma low-density lipoprotein-cholesterol (r = -0.75; P < 0.01). It is concl uded that human PLTP catalyses exchange/transfer processes of alpha-T between lipid compartments. This factor may be of relevance in atherog enesis and tumour initiation and growth.