Soluble enzyme system for vitamin K-dependent carboxylation.

The vitamin K-dependent carboxylating system has been solubilized by Lubrol PX or Triton X-100 treatment of vitamin K-deficient rat liver microsomes. As obtained from vitamin K-deficient rat liver, this soluble preparation is dependent upon the in vitro addition of vitamin K1 for carboxylating activity. The enzyme system is complex and is dependent upon NADH and dithiothreitol for maximum activity. While detergents used to solubilize the enzyme complex do markedly inhibit the activity of the system, the solubilized system is still highly responsive to vitamin K addition and can be used for further study of the carboxylating enzyme system. The requirement for dithiothreitol and the inhibition by p-hydroxymercuribenzoate indicate the involvement of an --SH enzyme in the carboxylating system.     

Fine needle aspiration cytology of fibrolamellar hepatocellular carcinoma

The major cytologic features seen in fine needle aspirates from two cases of fibrolamellar hepatocellular carcinoma were: liver-like tumor cells, characterized by plump, polygonal forms with eosinophilic, granular cytoplasm; large oval nuclei with extremely prominent solitary nucleoli; and parallel bands of fibrous tissue and fibrocytes seen within the tumor fragments. Other helpful features included intracytoplasmic hyaline globules and well-delineated pale bodies. Clinically, the tumors occurred in young patients with noncirrhotic livers and ran a more favorable course than do other types of hepatocellular carcinoma.     

Metabolism of cationized lipoproteins by human fibroblasts: biochemical and morphologic correlations

Human plasma low density lipoprotein (LDL) that had been rendered polycationic by coupling with N, N-dimethyl-1, 3-propanediamine (DMPA) was shown by electron microscopy to bind in clusters to the surface of human fibroblasts. The clusters resembled those formed by polycationic ferritin (DMPA-feritin), a visual probe that binds to anionic site on the plasma membrane. Biochemical studies with (125)I-labeled DMPA-LDL showed that the membrane-bound lipoprotein was internalized and hydrolyzed in lysosomes. The turnover time for cell bound (125)I-DMPA-LDL, i.e., the time in which the amount of (125)I-DMPA-LDL degraded was equal to the steady-state cellular content of the lipoprotein, was about 50 h. Because the DMPA-LDL gained access to fibroblasts by binding nonspecifically to anionic sites on the cell surface rather than by binding to the physiologic LDL receptor, its uptake failed to be regulated under conditions in which the uptake of native LDL was reduced by feedback suppression of the LDL receptor. As a result, unlike the case with native LDL, the DMPA-LDL accumulated progressively within the cell, and this led to a massive increase in the cellular content of both free and esterified cholesterol. Studies with (14)C-oleate showed that at least 20 percent of the accumulated cholesteryl esters represented cholesterol that had been esterified within the cell. After 4 days of incubation with 10 μg/ml of DMPA-LDL, fibroblasts had accumulated so much cholesteryl ester that neutral lipid droplets were visible at the light microscope level with Oil Red O staining. By electron microscopy, these intracellular lipid droplets were observed to lack a tripartite limiting membrane. The ability to cause the overaccumulation of cholesteryl esters within cells by using DMPA-LDL provides a model system for study of the pathologic consequences at the cellular level of massive deposition of cholesteryl ester.     

TOTAL LIPID PRODUCTION OF THE GREEN ALGA NANNOCHLOROPSIS SP. QII UNDER DIFFERENT NITROGEN REGIMES1

The green alga Nannochloropsis sp. QII was cultivated in media with sufficient and growth-limiting levels of nitrogen (nitrate). Nitrogen deficiency promoted lipid synthesis yielding cells with lipids comprising 55% of the biomass. The major lipids were triacylglycerols (79%), polar lipids (9%) and hydrocarbons (2.5%). The polar lipids consisted of a broad range of phospholipids, glycolipids and sulfolipids. Other lipids identified were pigments, free fatty acids, saponifiable and unsaponifiable sterol derivatives, various glycerides, a family of alkyl-1, 4-dioxane derivatives and a series of alkyl- and hydroxyalkyl-dimethyl-acetals. Experiments in which ¹⁴CO₂ was provided at different times in the growth cycle demonstrated that enhanced lipid biosynthesis at low nitrogen levels resulted principally from de novo CO₂ fixation.