HDL-induced cardiac prostacyclin synthesis: relative contribution of HDL apoprotein and lipid

The objective of this study was to determine if the apoprotein or lipid constituents of high density lipoproteins (HDL) mediate HDL-induced prostacyclin synthesis in the Langendorff-perfused rabbit heart. Acetylation, acetoacetylation, or partial removal by trypsin digestion of HDL apoprotein did not reduce the ability of the lipoprotein to stimulate cardiac prostacyclin synthesis. Delipidated apoproteins were less effective in stimulating cardiac prostacyclin synthesis in comparison to intact HDL. In contrast, protein-free lipid vesicles, made from HDL lipids, caused a pronounced stimulation of cardiac prostacyclin synthesis. These results suggest that HDL apoproteins, in their native state, are not essential for HDL-induced cardiac prostacyclin synthesis. The stimulation of cardiac prostacyclin synthesis by HDL may depend on the lipoprotein's lipid rather than on its apoprotein constituents.     

Mechanism of the binding of 2-(4'-hydroxyphenylazo)benzoic acid to bovine serum albumin

The mechanism of the binding of 2-(4'-hydroxyphenylazo)benzoic acid (HABA) to bovine serum albumin was studied by relaxation methods as well as the binding isotherm using gel chromatography. A single relaxation was observed over a wide range of HABA concentration except at the extremes of high concentration where another slow process was observed. The concentration dependence of the reciprocal relaxation time of the fast process decreased monotonically with increase in concentration of HABA at constant polymer concentration. The data were analyzed on the basis of Brown's domain structure model and were found to be consistent with a sequential binding mechanism. The azohydrazon tautomerism of HABA was identified with the intramolecular step of the complex. The activation parameters of the step, determined from the temperature dependence of the relaxation time of the fast process, showed that this step is rate limited by an enthalpy barrier in both forward and backward directions. Comparison of the activation parameters with those of other serum albumin-ligand systems suggests that there is an enthalpy-entropy compensation in the activation process of the intramolecular step with the compensation temperature at about 270 K; the enthalpy-entropy compensation is thought to be related to the hydrophobic nature of the ligand.     

Morphological changes in the cochlear nuclear complex in primate phylogeny and development

The primate cochlear nuclear complex exhibits several characteristic morphological differences in the various primate families from Lorisidae through Hominidae. The most striking differences occur in the organization of the dorsal cochlear nucleus in which the laminar pattern becomes progressively obscured. Granule cells form an external granular layer as well as being intermixed within the molecular and pyramidal layers in slow lorises and squirrel and rhesus monkeys. Whereas a prominent external granular layer remains in chimpanzees, granule cells are scant in other portions of the nucleus. Human adults lack an external granular layer. A small number of granule cells occur but with inconstant distribution. Primates lack the linear array of pyramidal cells oriented perpendicularly to the epithelial surface as seen in cats. The granule cell layer exhibits similar regression in development of the human cochlear complex. The external granular layer is prominent in the fetus but rapidly decreases in size after birth. It achieves its adult form prior to 18 months. The data suggest that neuronal attrition, or programmed cell death, may be the major mechanism accounting for the alterations that occur in the human granule cell layer. Other differences in cytoarchitecture, within the great apes and humans, include decreases in the small and giant cell populations of the cochlear complex. These changes, in consort with the organizational changes and reduction of granule cells as noted above, suggest a trend towards reduced intranuclear integration at the level of the cochlear nucleus coupled with encephalization of the auditory system.     

The distribution of carbohydrate side chains along the polypeptide chain of glucoamylase

Glucoamylase is a starch-hydrolyzing enzyme with a glycoprotein structure, used industrially for the conversion of starch to glucose, citric acid, corn syrups, and high-fructose sweeteners. This enzyme possesses an unusual type of structure in which many carbohydrate side chains are linked O-glycosidically to serine and threonine residues of the polypeptide chain. The carbohydrate side chains may be single monosaccharide residues or oligosaccharides of mannose, glucose, galactose, and in some cases N-acetylglucosamine. New data from experiments on the CNBr fragmentation of glucoamylase followed by chemical and immunological characterization of the fragments show that the carbohydrate side chains are distributed randomly along the polypeptide chain. Such a structure is appropriately termed a random model reprensentation for the glucoamylase molecule.     

A composite transposon 3'' to the cow fetal globin gene binds a sequence specific factor.

Two unusual sequence organizations were found within the beta-globin locus of the cow. Each was a composite, consisting of closely linked Alu-type repeats with a short stretch of genomic non-repetitive sequence, called a lagan, sandwiched between. One lagan was found 3' to the fetal globin gene, while the second lay between the adult globin gene and a globin pseudogene. Southern blot analysis indicated that both lagans appeared twice within the cow haploid genome, with the second copies lying outside the cow beta-globin locus. One of these non-globin locus homologues was cloned and subjected to sequence analysis. Comparison of the DNA sequence data showed that the lagan-Alu composite was transposed as a unit. The lagan 3' to the cow fetal globin gene contains the recognition site for a sequence specific DNA binding factor. This factor was present in extracts from fetal, but not from adult cow tissues.     

Avian hepatic T3 generation by 5'-monodeiodination: characterization of two enzymatic pathways and the effects of goitrogens

The enzymatic nature of 5'-monodeiodination (5'-D) in avian liver homogenates was demonstrated by abolishment of activity by iopanoic acid (IOP). T3 production from T4 was dependent on enzyme and substrate concentrations, incubation time, incubation temperature, and pH. Two pathways of 5'-D activity were present in avian liver and exhibited characteristics similar to those described in mammalian tissues. Type II activity was identified as propylthiouracil (PTU)-insensitive activity. Type I (PTU-sensitive) was determined by difference between Total and Type II. Km values were 1.58 microM T4 for Total activity and 0.90 nM T4 for Type II, corresponding to the characteristics of the mammalian pathways. The effects of goitrogens on avian hepatic 5'-D were equivalent to those reported for the mammalian enzyme.     

Conformational study of 13C-enriched fibroin in the solid state, using the cross polarization nuclear magnetic resonance method

Silk fibroin with the alanyl carboxyl carbon enriched with 13C was obtained by giving a diet containing 13C-enriched alanine to the larvae of Bombyx mori and Antheraea pernyi at the fifth instar. Sericin-free fibroin fibers were prepared from cocoons, and gut was made from the liquid silk in the gland. The final 13C content was about 13%. Cross polarization/magic angle sample spinning spectra at 25 MHz and 75 MHz were measured for each sample at different orientations. Spectra were simulated using the principal values and orientations of the shielding tensor in the alanine crystal. The results indicate that the beta-structure of the fibroin may be a little more flattened than the typical pleated sheet beta-structure.     

An active site-tyrosine-containing heptapeptide from D-amino acid oxidase

The flavoenzyme D-amino acid oxidase (Eo) is rapidly chlorinated by N-chloro-D-leucine (Rudie, N.G., Porter, D.J.T., and Bright, H.J. (1980) J. Biol. Chem. 255, 498-508). We have carried out chymotryptic digestion of E0-36Cl2 and find that all of the radiolabel is located in a heptapeptide having [3.5-36Cl2]chlorotyrosine as the COOH-terminal residue. This heptapeptide, having the sequence -Asp-Leu-Glu-Arg-Gly-Ile-Tyr-, is located within a larger fragment obtained previously from cyanogen bromide cleavage of E0. These results demonstrate that the target for chlorination in E0 must be a single tyrosine residue and provide, when taken together with previous findings, the first clear evidence for the identity and location of an active site residue in the polypeptide chain of D-amino oxidase.