CHARACTERIZATION AND DEVELOPMENTAL CHANGES OF UDP-GALACTOSE-CERAMIDE GALACTOSYL TRANSFERASE IN A RAT CNS AXOLEMMA-ENRICHED FRACTION. DIFFERENCES AND SIMILARITIES OF THE ENZYME ASSOCIATED WITH THE MICROSOMAL AND MYELIN FRACTIONS

Abstract— The properties of rat CNS UDP-galactose-ceramidc galactosyltransferase in an axolemma-enriched fraction (AXL), microsomes, and myelin simultaneously isolated with the AXL was characterized using a newly developed assay system. The microsomal enzyme utilized either magnesium or manganese equally well as the divalent cation at 3.3 m m , while both the myelin and AXL enzyme preferred manganese over magnesium at this concentration. The microsomal enzyme was more stable to heat inactivation than the myelin or AXL enzyme. The AXL galactosyltransferase had the highest specific activity at 15 days (8-fold higher than that of the microsomes) and dramatically decreased in specific activity with development. The developmental profile of the myelin enzyme paralleled that of the AXL although the absolute specific activity was lower than that of AXL. In contrast, the specific activity of microsomal enzyme was quite low at the earliest age then sharply increased to 25 days and gradually decreased with further development. The specific activity of the enzyme in AXL isolated from Quaking mouse was dramatically decreased (about 5% of control levels) whereas both whole homogenate and microsomal specific activity were decreased to 35% of control levels. These data indicate that AXL and myelin contain a galactosyltransferase with properties which are unique relative to those of the microsomal fraction. The possible functional significance of these findings with respect to myelination is discussed.     

The aglomerular nephron of antarctic teleosts: a light and electron microscopic study.

Complete serial sections demonstrated that ten species of Antarctic teleost fishes representing two families had aglomerular kidneys. The aglomerular nephron of such kidneys consists of two distinct regions: (1) a highly contorted principal segment and (2) a system of collecting tubules and ducts. Throughout the principal segment the cells are characterized by densely packed microbilli and a single cilium projecting into the lumen. Within the cytoplasm, lysosomes are rarely encountered, as would be expected if there is little or no reabsorption of protein from the urine. At the base of these cells, the plasma membrane is prominently infolded in close association with abundant mitochondria. The overall fine structure of the principal segment cells is consistent with their probable function in the secretion of ions into the formative urine. Between the principal segment and the collecting tubule is a very short transitional zone characterized by transitional mucus cells and multiciliated cells. The collecting tubule and duct system is lined entirely by mucus cells. In comparison with principal segment cells, the mucus cells have a well-developed Golgi complex and abundant secretory granules in the apical cytoplasm; these granules presumably contain the non-sulfated acid mucopolysaccharide demonstrable by light microscopic histochemistry.     

Seasonal cycles of diversity and similarity in a Central American rainforest butterfly community

Despite the importance of understanding the effects of tropical seasonality on ecological diversity, few studies have investigated the influence of environmental factors on seasonal community composition, and even fewer use standardized sampling and robust analytical methods that are directly comparable. Our 104 months of sampling in Costa Rican lowland rainforest yielded 12 757 individuals of 106 fruit‐feeding butterfly species demonstrated biannual cycles in species diversity, but community similarity showed an annual cycle that peaked in the driest months. We found that community diversity and similarity did not decline with increasing time lag, which we attribute to lack of long‐term changes in species abundances. Our findings differ from a similar study in Ecuador, where cycles in weather and community diversity were annual. Long‐term intensive monitoring and robust statistical analysis of changes in community composition in relation to environmental factors can help to elucidate the dynamics of communities, and their response to climate change.     

Mucin biosynthesis. Enzymic properties of human-tracheal epithelial GDP-L-fucose:beta-D-galactoside alpha-(1----2)-L-fucosyltransferase

The human-tracheal, epithelial alpha-(1----2)-L-fucosyltransferase that transfers L-fucose from GDP-L-fucose to an acceptor containing a beta-D-galactopyranosyl group at the nonreducing terminal was characterized. Optimal enzyme activity was obtained at pH 6.5. 20-30mM MnCl2 (or CaCl2), and 0.05% Triton X-100 or 0.5% Tween 20. Mg2+ and Ba2+ ions moderately enhanced the enzyme activity, whereas Fe2+, Co2+, Zn2+, and Cd2+ ions were inhibitory. The enzyme activity was inhibited by N-ethylmaleimide and nucleotides of guanine, inosine, xanthine, and uridine. However, ATP and dithiothreitol did not affect the enzyme activity. The apparent Michaelis constant for GDP-L-fucose, freezing point-depressing glycoproteins (expressed as Gal----GalNAc----Thr), and phenyl beta-D-galactopyranoside was 0.29, 5.70, and 25.4mM, respectively. Under alkali-borohydride conditions (0.05M NaOH-M NaBH4, 45 degrees, 20 h), an L-[14C]fucosyltrisaccharide was released from the product obtained by use of freezing point-depressing glycoprotein as the acceptor. The alpha-L anomeric configuration of the fucoside was determined by the release of L-[14C]fucose from the purified trisaccharide by Turbo cornutus alpha-L-fucosidase. The (1----2) linkage of the L-fucosyl group to the D-galactosyl residue was established by methylation technique (m.s.-g.l.c.). The present enzyme has properties similar to those of the human milk alpha-(1----2)-L-fucosyltransferase which is encoded by a secretor gene.