Lipoprotein particles from the Golgi apparatus of guinea-pig liver

1. A cell fraction has been isolated from guinea-pig liver and shown to be rich in Golgi apparatus by electron microscopy. The activity of UDP-d-galactose-N-acetylglucosamine galactosyltransferase was over 100-fold greater in this cell fraction than in the liver homogenate. These data support the conclusion that the fraction was enriched in Golgi apparatus. 2. The Golgi cisternae and secretory vesicles contained electron-dense particles of 10-80nm diameter. Disruption of the Golgi apparatus cell fraction released these particles, which were separated into VLD (very-low-density) and LD (low-density) species on the basis of their density. 3. The Golgi VLD particles possessed morphological, flotational, chemical and immunochemical properties which closely resembled those of the serum VLD lipoproteins from the same animals. 4. The Golgi LD particles were rich in phospholipid, containing 48.1% by weight. The chemical composition of these particles was quite distinct from that of the serum LD lipoproteins, but did, however, show some similarity to that of the serum VLD lipoproteins. A marked resemblance was noted in the chemical characteristics of the Golgi LD and VLD particles (with the exception of triglyceride content). In addition, these two species of Golgi particles possessed the same antigenic determinant. 5. The results suggest that the Golgi VLD particles are the precursors of the serum VLD lipoproteins. On the basis of similarities in gross chemical composition and in the antigenic determinant of the Golgi LD and VLD particles, we conclude that the LD particles are probably the precursors of the VLD particles. In view of the marked differences in gross chemical composition of the Golgi LD particles and serum LD lipoproteins, it appears unlikely that the LD particles are directly secreted into the serum pool.

THE NATURE AND OCCURRENCE OF PRE-BETA-LIPOPROTEIN IN DIABETIC CHILDREN AND PREGNANT WOMEN. AN ELECTROPHORETIC AND ULTRACENTRIFUGAL STUDY OF SERUM LIPOPROTEINS

A marked increase in pre-beta-lipoprotein was found in eleven of twenty-one untreated diabetic children and six of twenty treated diabetic children. In both diabetic and nondiabetic pregnant women there was a steady increase in the amount of this lipoprotein after the sixteenth week of pregnancy whereas earlier in pregnancy a marked increase was found only in a small group of diabetic women (five of fifty-two).

A detailed study of the nature of pre-beta-lipoprotein showed that the protein moiety is immunochemically the same as that of beta-lipoprotein, but that the lipid moiety contains more triglyceride and less cholesterol than that of beta-lipoprotein. Pre-beta-lipoprotein as defined by paper electrophoresis was found, on ultracentrifugal separation using the salt density gradient method, to have a flotation rate of Sf15–100. Paper electrophoresis provides a useful though rough means of recognizing excessive amounts of this lipoprotein. A marked pre-beta band suggests the presence of more than 125 mg. per 100 ml. of Sf15–100 lipoprotein-lipid.

Studies of the lipid composition of Sf15–100, 10–15, 3–9 and high-density lipoproteins showed that, for each fraction, the lipid composition remains constant irrespective of the amount of total lipid within the fraction and irrespective of whether the individual is diabetic or nondiabetic, pregnant or nonpregnant.

Immunologic studies of human high density lipoproteins

High density serum lipoprotein underwent serologic and physicochemical alterations on aging during storage at 0 degrees C. for 1 month, as judged by decrease of diffusion coefficient and increase of C' fixation. Ultracentrifugation, dialysis, and high concentrations of sodium chloride did not cause these changes. A protein sedimenting at density 1.24 in the ultracentrifuge reacted with antiserum to high density lipoprotein. Probably it was the protein portion of alpha lipoprotein dissociated from the lipide during ultracentrifugation. Although the antiserum to high density lipoprotein did not react with low density lipoprotein prepared from normal serum, it reacted with similarly prepared lipoproteins from the serum of a patient with biliary cirrhosis.