Structural and functional properties of human and mouse apolipoprotein A-I.

Mouse and human plasma apolipoprotein A-I (apo A-Im and apo A-Ih, respectively) were investigated to compare their molecular properties in solution, their incorporation into palmitoyloleoylphosphatidylcholine-apo A-I (POPC-apo A-I) discoidal complexes; their structural stability in discoidal complexes and high-density lipoproteins (HDL), and their effect on structural rearrangement of discoidal complexes upon interaction with low-density lipoproteins (LDL). Unlike apo A-Ih, only minimal concentration-dependent self-association was observed for apo A-Im. While both apo A-Im and apo A-Ih formed discoidal complexes of distinct composition and size that reflected reassembly molar ratios of POPC/apo A-I, apo A-Im demonstrated specific deficiencies in formation of larger-sized complexes. Denaturation of both apo A-Im- or apo A-Ih-containing complexes and HDL with guanidine hydrochloride (GuHCl) indicated significantly reduced stabilization of apo A-Im by lipid in these particles. Interaction of apo A-Im- or apo A-Ih-containing discoidal complexes with human plasma LDL revealed a more extensive conversion of apo A-Im-complexes to smaller species. Mean hydrophobicities and mean hydrophobic moments of amphipathic helical segments in apo A-Im and apo A-Ih were compared; differences potentially contributing to differential lipid-binding properties between apo A-Im and apo A-Ih were identified. Our results demonstrate differences between apo A-Im and apo A-Ih that may contribute to the major changes in plasma HDL distribution and function observed in apo A-Ih transgenic mice.

Effect of LDL and serum from diabetic subjects on DNA synthesis in HIT-cells in culture.

The effect of lipoprotein-deficient serum (LPDS) with and without added low-density lipoprotein (LDL), isolated from diabetic subjects, on the replication of SV40-transformed islet cells (HIT cells) was investigated. Whole serum as well as LPDS preparations stimulated DNA synthesis maximally when added to the culture medium at a final concentration of 0.1%. The addition of LDL at 25 and 175 micrograms protein/ml medium did not cause further stimulation. On the contrary, the higher concentrations resulted in a significant inhibition. These results suggest that previously observed stimulation of DNA synthesis in smooth muscle cells by LDL from diabetic subjects is most likely due to the presence of growth factors in the serum of these patients and not to LDL per se.

Apolipoprotein-lipid association in oxidatively modified HDL and LDL.

We investigated the effect of Cu2+ catalyzed peroxidation on the status of tryptophan (Trp) in protein moieties in HDL and LDL together with its effect on apolipoprotein-lipid association. Incubation of HDL with Cu2+ resulted in a rapid decrease of Trp fluorescence intensity with time with a concomitant increase in Trp maximum emission wavelength (lambda max). LDL incubated with Cu2+ also showed a rapid decrease in Trp fluorescence intensity with time, with no associated increase in lambda max. The status of apo HDL and apo LDL was investigated after 4 h oxidation (4h-oxHDL and 4h-oxLDL respectively). With 4h-oxHDL, the shift in lambda max was not associated with protein dissociation but rather with protein crosslinking and formation of larger HDL species. Progressive increase in lambda max was observed in 4h-oxHDL with increase in guanidine hydrochloride (GuHCl) concentration; this was not due to protein dissociation. Although oxidation of LDL did not produce an increase in lambda max, a significant increase in wavelength was observed when 4h-oxLDL was exposed to increasing concentration of GuHCl. SDS-polyacrylamide gel electrophoresis and nondenaturing gradient gel electrophoresis of the 4h-oxLDL indicated formation of smaller molecular weight protein fragments that were still associated with LDL. Ultracentrifugation of oxidized LDL in the presence and absence of GuHCl showed no dissociated protein. In summary, these data indicate the following: (a) lipid peroxidation has a direct effect on Trp residues in both HDL and LDL, (b) oxidation of HDL is associated with conformational change in apo HDL, crosslinking and formation of larger particles, (c) oxidized HDL have a more stable apolipoprotein-lipid association than native HDL, (d) oxidation of LDL is associated with changes in apo B, that by fluorescence are apparent only in presence of GuHCl and results in fragmentation of apo B without dissociation of protein or change in particle size, and (e) stability of apolipoprotein-lipid association is comparable in oxidized and native LDL.

Gamma glutamyl transferase in diabetic rats. The effect of insulin treatment.

In rats, streptozotocin-induced diabetes resulted in the increase of plasma gamma GT. A daily dose of 2 U protamine zinc insulin for two weeks did not affect the high levels of both gamma GT and glucose. Supplementation with 3 U insulin for only one week reduced both gamma GT and glucose levels. This indicates that insulin treatment could correct the rise of the enzyme level found in some diabetic patients.

Plasma lipid and lipoprotein concentrations in an Egyptian male sample.

The distributions of plasma total cholesterol and triglyceride levels as well as plasma lipoprotein abnormalities were studied in 50 Egyptian males aged 20-69 years. Total cholesterol increased gradually with advancing age up to the seventh decade. In contrast, triglycerides peaked in the fifth decade, then declined. Type IV lipoprotein pattern was the most common abnormality (12%). Type II was less common (2.0%). Types I, III and V were not encountered. The mean plasma triglyceride and cholesterol levels were not markedly different from similar studies done on non-Arab populations. The high incidence of hyperlipidemia among this group is worth noting, especially in the search for the coronary-prone, since all of the type IV group had normal total cholesterol levels.

Aconitase from the oyster Crassostrea virginica.

1. The presence of aconitase activity in the oyster. Crassostrea virginica, has been demonstrated. 2. Low levels of activity were found in the different tissues with highest level in digestive diverticular and lowest level in muscle. 3. The conversion of both citrate and iso-citrate to cis-aconitate suggests the presence of an enzyme system capable of utilizing these compounds at a slow but demonstrable rate to give classically expected results. 4. Comparison of the oyster enzyme with aconitase from mammalian tissue indicated great similarity between the two enzyme systems.

Extraction of lipids from mammalian liver using nontoxic solvents.

A simple method for extracting and purifying lipids from rat liver in a single step using nontoxic solvents is described. The method consists homogenizing the pulverized tissue with a mixture of trichlorotrifluoroethane (Cl2CF-CCIF2) and isopropyl alcohol (1 : 1, v/v). Just enough water is added to the lipid extract to produce a biphasic system. Pure lipid extract is obtained by isolating the lower layer from the aqueous upper phase which contains the non-lipid materials. The described method compares favourably with that of Folch et al., both quantitatively. The solvent system used also has the advantage of being less toxic than the widely used chloroform/methanol system, which makes it safer for prolonged use. The new method is simple, efficient and reproducible.