Rational construction of a 2-hydroxyacid dehydrogenase with new substrate specificity

Using site-directed mutagenesis on the lactate dehydrogenase gene from Bacillus stearothermophilus, three amino acid substitutions have been made at sites in the enzyme which we suggest in part determine specificity toward different hydroxyacids (R-CHOH-COOH). To change the preferred substrates from the pyruvate/lactate pair (R = -CH3) to the oxaloacetate/malate pair (R = -CH2-COO-), the volume of the active site was increased (thr 246----gly), an acid was neutralized (asp-197----asn) and a base was introduced (gln-102 - greater than arg). The wild type enzyme has a catalytic specificity for pyruvate over oxaloacetate of 1000 whereas the triple mutant has a specificity for oxaloacetate over pyruvate of 500. Despite the severity and extent of these active site alterations, the malate dehydrogenase so produced retains a reasonably fast catalytic rate constant (20 s-1 for oxaloacetate reduction) and is still allosterically controlled by fructose-1,6-bisphosphate.     

Immunogenicity and antigenicity of immunoglobulins: detection of human immunoglobulin light-chain carbohydrate, using concanavalin A

Concanavalin A binding to glycoprotein bands on nitrocellulose blots was used to detect mannose, sorbose, N-acetylgalactosamine and/or glucose residues on 100% (31/31) of human Bence Jones protein light chains, following sodium dodecyl sulphate-polyacrylamide gel electrophoresis. All (20/20) light chains form IgG myeloma proteins and light chains from a preparation of normal polyclonal human IgG were also bound by concanavalin A. The specificity of concanavalin A for glycoproteins was demonstrated by its binding to human Fc fragments and a human monoclonal anti-Rhesus D antibody (REG-A), but not to human albumin pFc' fragments and aglycosylated REG-A derived from cells grown in the presence of the glycosylation inhibitor tunicamycin. These results suggest that all Bence Jones proteins and light chains from myeloma IgG proteins contain mono- or oligosaccharides linked O-glycosidically to serine or threonine residues.     

The effect of sucrose on the levels of abscisic acid, indoleacetic acid and zeatin/zeatin riboside in wheat ears growing in liquid culture

The influence of a varied sucrose supply on grain size and hormonal contents of detached wheat ears ( Triticwn aestivum L. cv. Schirokko) was investigated throughout grain development. In ears led limited amounts, or no sucrose, grain weights in both proximal and distal grain positions of the ear were reduced. Radioimmunoassay for abscisic acid, indoleacetic acid and zeatin/zeatin riboside showed that the changes in the levels of these hormones in grains and bracts were comparable to intact ears when detached ears were well supplied with sucrose. Under conditions of limited sucrose supply, higher abscisic acid levels in the distal and proximal grains of detached ears were found compared to ears supplied with adequate sucrose. Limiting sucrose supply to the ear did not alter the levels of indoleacetic acid or zeatin/zeatin riboside in either the grains or bracts of detached ears.     

Physiological integration in Cassia fasciculata Michx.: inflorescence removal and defoliation experiments

Summary In the annual herb Cassia fasciculata virtually every leaf subtends an axillary inflorescence. We examined the degree to which these leaf-inflorescence units (reproductive nodes) were physiologically independent of each other in the production of flowers, fruits, and seeds. Removal of up to 4 of every 5 inflorescences resulted in substantial increases in fruit and seed production by remaining, intact reproductive nodes. These increases nearly compensated for and manipulated reproductive nodes were associated with different vascular strands. When 2 of every 3 leaves were removed, fruit and seed production were reduced at both intact and defoliated reproductive nodes. Taken together, these results suggest that neighboring reproductive nodes in C. fasciculata are not physiologically independent of one another, and that competition among fruits and seeds for parental resources occurs over several reproductive nodes.Scientific contribution no. 1595 from the New Hampshire Agricultural Experiment Station     

Evolutionary conservation of the human homologue of the yeast cell cycle control gene cdc2 and assignment of Cd2 to chromosome 10

Summary The human homologue of the fission yeast Schizosaccharomyces pombe cell cycle control gene cdc2 has been assigned to chromosome 10. DNA hybridization reveals that this gene is highly conserved in vertebrates. The human CDC2 gene probe detects a simple two-allele polymorphism in Taq1-digested DNA.     

Studies on the submicrosomal fractions of bovine oligodendroglia: Lipid composition and glycolipid biosynthesis

Oligodendroglia were isolated from bovine brain, and a crude, microsomal fraction obtained from cell homogenates was subfractionated into myelin (MP), plasma membranes (PM), Golgi (GF), smooth (SER) and rough (RER) endoplasmic membranes using discontinuous-sucrose gradient centrifugation. The submicrosomal fractions were characterized by ultrastructural examination and analysis of the specific organelle markers. The myelin and plasma membrane rich fractions contained characteristically the highest amounts of the lipid with lower mole percentages of total phospholipids and phosphatidylcholine, and higher concentrations of phosphatidylethanolamine (+plasmalogens), cholesterol and galactolipids. Considerable amounts of the typical myelin galactolipids (galacto-cerebrosides, sulfatides and monogalactosyl diglycerides) were also found in the Golgi fraction (GF). The GF fraction had the greatest enrichment of glycolipid-forming galactosyltransferases, and the distribution of these enzymes correlated well with that of the Golgi marker enzymes. The results give evidence that intracellular Golgi apparatus of oligodendroglia is rich in the myelin-specific lipids, and suggest its involvement in the synthesis and processing of myelin lipids.     

Effect of dietary protein on cholesterol homeostasis in diabetic rats

Normal and streptozotocin (STZ)-diabetic rats were studied in order to examine the effects of altering the type of dietary protein on cholesterol homeostasis. Rats were fed a non-purified or a purified diet containing either casein or soybean protein. The results obtained on the specific aspects of lipid metabolism were remarkably similar in control rats fed the non-purified (Purina Lab Chow) diet or the purified diet with the soybean protein. However, most of the findings obtained with the above two groups were different from those obtained with rats fed the purified diet containing casein. In the latter group, plasma cholesterol was elevated following a 15-day feeding period as compared to the other two dietary groups. The excess plasma cholesterol in the casein-fed group was found in two lipoprotein fractions with densities of 1.023-1.045 g/ml and 1.045-1.086 g/ml, respectively. The latter lipoprotein fraction was also enriched with apolipoprotein E. The casein-fed animals also showed a lower fractional rate of plasma cholesterol esterification and an abnormal accumulation of cholesterol in the body despite inhibition of cholesterol synthesis in the liver and in the intestines. Twelve to 15 days after the induction of diabetes, plasma cholesterol increased to a similar extent in the rats on all three diets. However, the distribution of cholesterol among the lipoprotein fractions was markedly different. The percentage of cholesterol in fractions of d less than 1.086 g/ml was increased while that carried in the fraction of d 1.086-1.161 g/ml decreased in the rats fed the nonpurified diet and the casein diet. In contrast, there was no change in the distribution of lipoprotein cholesterol between the diabetic and the control rats fed the soybean protein diet. The hepatic synthesis of cholesterol was unaltered in diabetic rats fed the nonpurified diet and the purified diet with soybean protein, but was increased 2.4-fold in diabetic rats fed casein. Intestinal cholesterol synthesis was increased in all three dietary groups. The increase was highest in the rats fed casein and lowest in rats fed soybean protein. The rate of sterol synthesis in the kidneys was not significantly affected by the diet or diabetes. In all three dietary groups diabetes led to an abnormal accumulation of cholesterol in the body. This accumulation was highest in the casein-fed rats and lowest in those fed the soybean protein diet. The cholesterol content of the kidneys was markedly increased by dietary casein.(ABSTRACT TRUNCATED AT 400 WORDS)     

Epitopes that span the tau molecule are shared with paired helical filaments

Tau protein has been shown to be an integral component of Alzheimer paired helical filaments (PHF). However, the extent to which tau is incorporated into PHF has not been clear because the antibodies used to label PHF generally do not have precisely defined epitopes. Here we define the antigenic sites for five monoclonal antibodies that react with tau and cross-react with SDS-extracted neurofibrillary tangles. The reactive sites were determined by screening a lambda gt11 sublibrary expressing small fragments of the tau sequence. The mapped epitopes were found to span almost the entire length of tau, suggesting that PHF contains tau in its entirety or nearly in its entirety. One antibody was found to cross-react with microtubule-associated protein 2, implying some degree of homology between the two proteins.     

Synthesis and biological activity of novel C-terminal-extended and biotinylated growth hormone-releasing factor (GRF) analogs.

A series of novel hGRF(1-29)-NH2 analogs were synthesized and biotinylated. The immunological and biological activities of these analogs were then characterized. To distance the biotin moiety from the putative bioactive core, a C-terminal spacer arm consisting of -Gly-Gly-Cys-NH2 (-GGC) was added to hGRF(1-29)-NH2 (hGRF29) and analogs, with subsequent biotinylation performed at the cysteine residue. Neither addition of the C-terminal spacer arm nor biotinylation affected affinity of these analogs for GRF antibody. Relative to hGRF(1-44)-NH2 (hGRF44: potency = 1.0), the biotinylated analogs were equipotent in vitro to their nonbiotinylated, parent compounds: [desNH2Tyr1,D-Ala2,Ala15]hGRF29-GGC-(tpBiocyt in)-NH2 (4.7) = [Ala15]hGRF29-GGC-(tpBiocytin)-NH2 (3.9) greater than hGRF29-GGC-(tpBiocytin)-NH2 (0.8). Based upon cumulative GH release data in vivo (0-60 min postinjection), [desNH2Tyr1,D-Ala2,Ala15]hGRF29-GGC-(tpBiocyt in)-NH2, [Ala15]hGRF29-GGC-(tpBiocytin)-NH2, and hGRF29-GGC-(tpBiocytin)-NH2 displayed 8.6, 5.5, and 0.8 times, respectively, the potency of hGRF44. These in vivo potency values were not significantly different from the corresponding parent compounds (i.e., with or without the C-terminal spacer arm). In summary, biotinylated hGRF analogs have been developed that retain full immunoreactivity and potent bioactivity (in vitro and in vivo), thus permitting their use in GRF receptor isolation, ELISA, and histochemical procedures.     

Rabbit and rat hepatic lectins have two sugar-combining sites per monomeric unit

Binding characteristics of the galactose/N-acetylgalactosamine-specific, hepatic lectins of rabbit and rat were studied using small, high-affinity ligands containing two and three N-acetylgalactosamine residues per molecule [Lee, R. T. and Lee, Y. C. (1987) Glycoconjugate J. 4, 317-328]. These N-acetylgalactosamine cluster ligands have the receptor-ligand dissociation constants in nanomolar range, so that the lectin-ligand interaction can easily studied by an equilibrium (gel chromatography) or non-equilibrium (fast filtration assay) method. The results suggest that there exist on the average two N-acetylgalactosamine-combining sites per monomeric unit of both the rabbit and rat lectins.