Two endocytic receptors, the low density lipoprotein (LDL) receptor (LDLR) and the LDLR-related protein (LRP) (7), and placed on ice. At the end of experiments, the abdominal cavity was exposed via a midline incision and a blood sample was drawn from the inferior vena cava. The portal vein was then cannulated with a 21-gauge needle, which was tied in place. The vena cava above the liver was then incised and the liver was flushed with 3 ml of cold 0.15 M NaCl under a pressure of 50 cm of water.The liver was then removed and weighed. A mixed endosome fraction was prepared by minor modifications of methods developed for rat liver (18). Two livers were pooled and homogenized in 0.5 M sucrose, and an endosome-enriched subcellular fraction was obtained after several steps by centrifugation in a Percoll gradient. This material was diluted with 2 vol of 0.15 M NaCI, and the endosomes were obtained by centrifugation onto a sucrose cushion. The fluffy white material just above the sucrose cushion was harvested with a Pasteur pipette, resuspended in 0.15 M NaCl, and recentrifuged as above. The purified endosomes were again harvested from just above the sucrose cushion for analysis. Their appearance by electron microscopy closely resembled that shown previously for hepatocytic endosomes from rats (18 RESULTSLDLR (-/-) mice had increased levels of cholesterol in LDL, as reported previously (7), and also in IDL, but only a slight increase in VLDL-cholesterol (Table 1). The concentrations of apoB-100 and apoB-48 in VLDL of normal and LDLR (-/-) mice were similar. The total concentration of apoB-100 in plasma, however, was increased almost 4-fold, mainly in LDL, and that of apoB-48 was increased only about 1.4-fold, also mainly in LDL, with a lesser increase in IDL. The concentration of apoE was increased 2.5-fold, predominantly in the LDL and IDL fractions, with a minor increase in VLDL.To determine the effectiveness of GST-RAP in blocking removal of activated a2-macroglobulin by the liver, the hepatic content of 125I was determined at intervals after intravenous

The multi‐layered microbial mats in the sand flats of Great Sippewissett Salt Marsh were found to have five distinct layers of phototrophic organisms. The top 1–3 mm contained oxygenic phototrophs. The lower 3–4 mm contained anoxygenic phototrophic bacteria. The uppermost gold layer contained diatoms and cyanobacteria, and chlorophyll a was the major chlorophyll. The next layer down was green and was composed of primarily filamentous cyanobacteria containing chlorophyll a. This was followed by a bright pink layer of bacteriochlorophyll b‐containing purple sulfur bacteria. The lowest layer was a thin dull green layer of green sulfur bacteria containing bacteriochlorophyll c. The distribution of the chlorophylls with depth revealed that two‐thirds of the total chlorophyll in the mat was composed of bacteriochlorophylls present in the anoxygenic phototrophys. The cyanobacterial layers and both purple sulfur bacterial layers had photoautotrophic activity. Light was attenuated in the uppermost layers so that less than 5% of the total radiation at the surface penetrated to the layers of anoxygenic phototrophys.

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