Probing the infrared quark mass from highly excited baryons.

We argue that three-quark excited states naturally group into quartets, split into two parity doublets, and that the mass splittings between these parity partners decrease higher up in the baryon spectrum. This decreasing mass difference can be used to probe the running quark mass in the midinfrared power-law regime. A measurement of masses of high-partial-wave Delta* resonances should be sufficient to unambiguously establish the approximate degeneracy. We test this concept with the first computation of excited high-j baryon masses in a chirally invariant quark model.

Displacement of apo A-I from HDL by apo A-II or its C-terminal helix promotes the formation of pre-beta1 migrating particles and decreases LCAT activation.

The displacement of apolipoprotein (apo) A-I by apo A-II is a major event in the remodeling of high density lipoproteins (HDL). In the present study, we investigated the displacement of apo A-I both from native and reconstituted HDL (rHDL) by either apo A-II or by the C-terminal helical peptide (i.e. residues 53-70). We studied the remodeling process of the original particles, the changes in size and composition and in their lecithin:cholesterol acyltransferase (LCAT) activating properties. Using gel filtration, we show that, at low apo A-II/AI ratios, the initial lipid apolipoprotein complex containing 2 mol apo A-I is remodeled into a mixed complex containing apo A-I and apo A-II, involving the displacement of one apo A-I by apo A-II. Upon addition of a larger amount of apo A-II, the rHDL particles become more heterogeneous and of larger size. Immunoblotting of the particles separated by non denaturing gradient gel electrophoresis shows that most of the apo A-I remains associated with the largest particles. The LCAT activation properties of the remodeled complexes decrease upon addition of either apo A-II or its C-terminal helix. This decrease is more pronounced when rHDL are incubated with the apo A-II C-terminal helix than with native apo A-II, as VmaX decreases from 28 to 16 and 7 nmol cholesteryl ester/ml per h respectively, whereas Km remains unchanged. The displacement of apo A-I observed with rHDL also occurred with native HDL particles as demonstrated by two-dimensional gel electrophoresis, using pyrene-phospholipid labeled HDL. Displacement of apo A-I generates pre-beta1 migrating particles containing apo A-I and phospholipids. We therefore propose that apo A-II has a dual effect on the role of HDL in reverse cholesterol transport: displacement of apo A-I from rHDL results in a negative control of the LCAT activity, while generation of pre-beta1 migrating particles enhances the formation of potential acceptors of cellular cholesterol.