Human lymphocytes treated with r-7,t-8-dihydroxy-t-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene require low-density lipoproteins for DNA excision repair

Human lymphocytes which were non-mitogen-stimulated, and which were depleted of lipoproteins, were found to be deficient in DNA excision repair typically initiated in these cells in response to treatment with a direct-acting polynuclear aromatic hydrocarbon carcinogen. Lymphocytes either depleted of lipoproteins or supplemented with human low-density lipoproteins formed DNA-carcinogen adducts which were not chromatographically distinguishable. The state of lipoprotein depletion did not alter lymphocyte uptake of thymidine from the medium. Lymphocytes which were depleted of lipoproteins, treated with carcinogen, and subsequently supplemented with low-density lipoproteins, regained the ability to engage in DNA excision repair. The data suggest that either low-density lipoprotein(s), or a component(s) of low-density lipoprotein(s), is required by human lymphocytes in order to initiate excision repair of carcinogen-damaged DNA.     

Nonvisual feeding in a visual planktivore,Xenomelaniris venezuelae

Summary Studies of the diel feeding patterns of the planktivorous fish, Xenomelaniris venezuelae, in Lake Valencia, Venezuela, revealed that, although the fish is primarily a diurnal feeder, it consumes substantial numbers of Chaoborus larvae and pupae at night. A number of fish species are known which feed on plankton at night, but these fish are filter feeders and their diets largely consist of relatively small, nonevasive prey. Chaoborus, however, is large and agile. Predation by Xenomelaniris in the dark was also studied experimentally. Captured fish were placed in completely darkened aquaria with zooplankton from Lake Valencia. After several hours the plankton was removed and examined for evidence of feeding. The fish were found to consume Chaoborus pupae and fourth instar larvae but not other types of prey. The mode of feeding by Xenomelaniris in the dark is unknown.     

Recognition of super-secondary structure in proteins

A procedure to recognize super-secondary structure in protein sequences is described. An idealized template, derived from known super-secondary structures, is used to locate probable sites by matching with secondary structure probability profiles. We applied the method to the identification of βαβ units in β/α type proteins with 75% accuracy. The location of super-secondary structure was then used to refine the original (Garnier et al., 1978) secondary structure prediction resulting in an 8.8% improvement, which correctly assigned 83% of secondary structure elements in 14 proteins. Slight modifications to the Garnier et al. method arc suggested, producing a more accurate identification of protein class and a better prediction for β/α. type proteins. A method for the incorporation of hydrophobic information into the prediction is also described.     

The effects of prey size, predator size, and sediment composition on the rate of predation of the blue crab, Callinectes Sapidus Rathbun, on the hard clam, MercenariaMercenaria (Linné)

Sediment preferences of blue crabs, Callinectes sapidus Rathbun, and predation rates on various size classes of the hard clam, Mercenaria mercenaria (Linné), in a variety of sediment types were studied in the laboratory. Blue crabs of all size classes exhibited a preference for sand, mud, and sand/mud rather than crushed oyster shell or granite gravel. Clams were more vulnerable to predation by crabs in sand and sand/mud than in crushed oyster shell or granite gravel. When crabs were given a choice of clam sizes based on carapace width (CW), small crabs (<75 mm CW) consumed 5- and 10-mm shell length (SL) clams. Medium crabs (75–125 mm CW) preferentially consumed 10-mm SL clams. Large crabs (> 125 mm CW) consumed 10- and 25-mm SL clams equally. Blue crabs did not eat clams that were >40-mm SL.     

Genetic Analysis of Murine Arylsulfatase C and Steroid Sulfatase

SWR/J mice possess two- to threefold higher 4-methylumbelliferyl sulfate (4MUS), dehydroepiandrosterone sulfate (DHEAS) and estrone sulfate (E1S) sulfatase activities in liver and kidney extracts than do A/J mice. These interstrain activity differences are maintained throughout the 6- to 45-day postnatal period. Characteristics of the hepatic activities of SWR/J mice suggest that all three activities reside in the same enzyme. Biochemical properties of the SWR/J and A/J enzyme were not significantly different. Expression of hepatic enzyme activity is subject to regulation by an autosomal locus possessing two alleles with additive effects. Postnuclear E1S- and DHEAS-sulfatase activities are primarily microsomal. Although postnuclear hepatic 4MUS-sulfatase activity is predominantly microsomal, renal activity is primarily nonmicrosomal. Only that portion of 4MUS-sulfatase occurring in cell membranes appears capable of hydrolyzing E1S and DHEAS. The hepatic- and renal-specific subcellular distributions of 4MUS-sulfatase activity may reflect tissue differences in enzyme processing. Renal 4MUS-sulfatase activity is also controlled by an autosomal gene with two alleles having additive effects. Positive correlation between hepatic and renal 4MUS-sulfatase activities indicates that both activities are most likely influenced by the same gene.     

Characterization of the Blood-Brain Barrier: Protein Composition of the Capillary Endothelial Cell Membrane

Microvessels were isolated from canine cerebral cortex, and the composition of the endothelial cell membrane was investigated. Endothelial cell membranes were separated from the surrounding basement membrane, solubilized, and subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis in 12% gels. Staining with Coomassie Blue revealed a characteristic banding pattern of at least 12 major proteins with apparent molecular weights between 14,000 and 250,000. When proteins from red blood cell ghosts were run simultaneously, no similarities were observed, except for proteins at apparent molecular weights of 43,000 (band 3) and 35,000 (band 4). These two proteins migrated exactly to the positions of the erythrocyte proteins actin and glyceraldehyde 3-phosphate dehydrogenase, respectively. Membrane glycoproteins in gels were also examined by the use of fluorescent lectins. Of the fluorescein isothiocyanate-conjugated (FITC) lectins tested, only FITC-concanavalin A had an affinity for any membrane components. Diazotized [125I]iodosulfanilic acid, a membrane-impermeable reagent, was used to label the internal (lumen) cell surface and the external (antilumen) cell surface. Autoradiography and determination of radioactivity levels in gel slices showed that several proteins were specifically labeled, and that major differences in radioactivity of proteins existed in internal and external labeling experiments. It is concluded that the protein composition of the luminal membrane is different from that of the antiluminal membrane.