Isolation and properties of nascent lipoproteins from highly purified rat hepatocytic Golgi fractions.

نویسندگان

  • R L Hamilton
  • A Moorehouse
  • R J Havel
چکیده

Two procedures were used to isolate hepatocytic Golgi fractions from rat liver. One procedure yields a light Golgi fraction (GF1 + 2) and the other "intact" stacks of cisternae. Triglyceride fatty acids in nascent very low density lipoproteins (VLDL) were labeled by injection of [3H]palmitate intravenously, and radiolabeled lipoproteins were injected as markers of potentially contaminating endosomes. GF1 + 2 fractions were enriched manyfold in the endosomal markers, indicative of substantial endosomal contamination, whereas intact Golgi fractions from the same livers were about 7% as contaminated. By electron microscopy, GF1 + 2 fractions contained mainly multivesicular bodies (MVBs), together with some Golgi-derived secretory vesicles. The small endosomal contamination of intact Golgi fractions was further reduced by a simple modification of the procedure, which removed most entrained endosomes. The surface constituents of Golgi VLDL (d less than 1.010 g/ml) released from these highly purified intact Golgi fractions differed from those of plasma VLDL. Golgi VLDL contained fivefold less unesterified cholesterol than plasma VLDL, but twofold more phospholipids. Golgi VLDL and plasma VLDL contained similar amounts of cholesteryl esters and triglycerides. The protein content of Golgi VLDL was substantially lower than that of plasma VLDL. ApoB-100 and apoB-48 were similarly represented, but nascent VLDL contained less of the C apolipoproteins. ApoA-I was present mainly as the proprotein in Golgi VLDL, but was virtually lacking in plasma VLDL. ApoE comprised about 22% of the protein mass of Golgi VLDL as well as plasma VLDL; the distribution of apoE isoforms was also similar. Apolipoproteins E and pro A-I released from ruptured Golgi cisternae were largely bound to the Golgi VLDL or were associated with Golgi membranes. Particles resembling low density lipoproteins (LDL) and high density lipoproteins (HDL) were not seen by electron microscopy in contents of intact Golgi fractions. These observations indicate that nascent Golgi VLDL are the primary particulate precursors of rat plasma lipoproteins of hepatocytic origin, and suggest that particles with the density of plasma HDL and LDL do not exist within the secretory pathway of normal hepatocytes. Thus, the results of this research on the properties of nascent plasma lipoprotein precursors contained within uncontaminated hepatocytic Golgi fractions differ substantially from previous published work.

برای دانلود رایگان متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

منابع مشابه

Apolipoprotein E localization in rat hepatocytes by immunogold labeling of cryothin sections.

The distribution of apolipoprotein (apo) E in rat hepatocytes was investigated with an affinity-purified polyclonal antibody raised against apoE isolated from hepatogeneous very low density lipoproteins (VLDL). The distribution of this antibody was visualized with colloidal gold complexed to anti-rabbit IgG. By epipolarization microscopy, apoE was found uniformly along the basolateral surfaces ...

متن کامل

Isolation and characterization of multivesicular bodies from rat hepatocytes: an organelle distinct from secretory vesicles of the Golgi apparatus

Hepatocytes of estradiol-treated rats, which express many low density lipoprotein receptors, rapidly accumulate intravenously injected low density lipoprotein in multivesicular bodies (MVBs). We have isolated MVBs and Golgi apparatus fractions from livers of estradiol-treated rats. MVB fractions were composed mainly of large vesicles, approximately 0.55 micron diam, filled with remnantlike very...

متن کامل

Assembly of very low density lipoproteins in rat

To investigate the assembly pathway for hepatic very low density lipoproteins (VLDL), nascent lipoproteins were recovered from a purified, intact rough endoplasmic reticulum (ER) fraction isolated from rat liver. Two fractions were recovered by ultracentrifugation. Particles isolated at d 1.006 g/ml were triglyceride-rich particles containing apolipoprotein (apo)B-100 or apoB-48, and apoE with ...

متن کامل

Assembly of very low density lipoproteins in rat liver: a study of nascent particles recovered from the rough endoplasmic reticulum.

To investigate the assembly pathway for hepatic very low density lipoproteins (VLDL), nascent lipoproteins were recovered from a purified, intact rough endoplasmic reticulum (ER) fraction isolated from rat liver. Two fractions were recovered by ultracentrifugation. Particles isolated at d 1.006 g/ml were triglyceride-rich particles containing apolipoprotein (apo)B-100 or apoB-48, and apoE with ...

متن کامل

GOLGI FRACTIONS PREPARED FROM RAT LIVER HOMOGENATES I. Isolation Procedure and Morphological Characterization

In devising a new procedure for the isolation of Golgi fractions from rat liver homogenates, we have taken advantage of the overloading with very low density lipoprotein (VLDL) particles that occurs in the Golgi elements of hepatocytes -90 min after ethanol is administered (0 .6 g/100 g body weight) by stomach tube to the animals . The VLDLs act as morphological markers as well as density modif...

متن کامل

ذخیره در منابع من


  با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید

عنوان ژورنال:
  • Journal of lipid research

دوره 32 3  شماره 

صفحات  -

تاریخ انتشار 1991