The 6R-oxygenase activity of arachidonate 5-lipoxygenase purified from porcine leukocytes

Arachidonate 5-lipoxygenase purified from porcine leukocytes was incubated with (5S)-hydroperoxy-6,8,11,14-eicosatetraenoic acid. In addition to degradation products of leukotriene A4 (6-trans-leukotriene B4 and its 12-epimer and others), (5S,6R)-dihydroperoxy-7,9,11,14-eicosatetraenoic acid was produced as a major product especially when the incubation was performed on ice rather than at room temperature. The amount of the (5S,6R)-dihydroperoxy acid was close to the total amount of leukotriene A4 degradation products. Under the anaerobic condition, production of the (5S,6R)-dihydroperoxy acid was markedly reduced. 5-Hydroxy-6,8,11,14-eicosatetraenoic acid could be a substrate of the enzyme and was transformed predominantly to a compound identified as (5S)-hydroxy-(6R)-hydroperoxy-7,9-trans-11,14-cis-eicosatetraenoic acid at about 1-2% rate of arachidonate 5-oxygenation. These findings indicated that the purified 5-lipoxygenase exhibited a 6R-oxygenase activity with (5S)-hydroxy and (5S)-hydroperoxy acids as substrates. The 6R-oxygenase activity, like the leukotriene A synthase activity, was presumed to be an integral part of 5-lipoxygenase because it required calcium and ATP and was affected by selective 5-lipoxygenase inhibitors.     

Sequence-specific modification of DNA by 6-hydroxybenzo[a]pyrene

6-Hydroxybenzo[a]pyrene cleaved phi X174 supercoiled DNA to open circular DNA in the presence of heavy metal ions. It induced an alkali-labile modification in DNA via an oxygen-radical-mediated reaction; the most frequent alkali-labile sites were on the 3' side of the pyrimidine residues of the pyrimidine cluster.     

Recessive Nonsense Suppressors in SACCHAROMYCES CEREVISIAE : Action Spectra, Complementation Groups and Map Positions

Three genes SUP111, SUP112 and SUP113 of Saccharomyces cerevisiae have been identified that can mutate to give recessive omnipotent nonsense suppressors. Alleles of these loci can also act as allosuppressors; that is, different phenotypes, due apparently to different efficiencies of suppression, can result from different alleles at a given locus. The SUP111, SUP112 and SUP113 loci map to the right arms of chromosomes VIII, VII and XIII, respectively.     

A putative met-enkephalin releaser, kyotorphin enhances intracellular Ca2+ in the synaptosomes

Kyotorphin (Tyr-Arg) at 1 to 100 microM increased the intracellular [Ca2+]i, determined with Quin-II in the slice and the entry of 45Ca2+ entry into synaptosomes of the lower brain stem of the rat. These effects were not antagonized by nifedipine nor verapamil. However, since this dipeptide caused no changes on the membrane potentials of the synaptosomes, measured with Rhodamine 6G, it is suggested that the kyotorphin-induced increase in the [Ca2+]i may be due not to effects on the voltage dependent Ca2+ channels and Na+-Ca2+ exchange mechanisms caused by the changes of the membrane potentials, but to the specific receptor (kyotorphin receptor)-mediated mechanisms.     

Unfolding rates of globular proteins determined by kinetics of proteolysis

A convenient method for the determination of unfolding rates of small globular proteins under physiological conditions was developed using digestion with proteases. The apparent first-order rate constants for digestion of lysozyme with thermolysin and with Pronase at pH 8 and 50 degrees C were shown to be saturated with increases of concentrations of these proteases. The maximum rate constants extrapolated were identical in digestions with two different proteases, and were found to be equal to the unfolding rate constant of lysozyme. Similarly, the unfolding rate constant of RNase A at pH 8 and 50 degrees C, and those of lysozyme, RNase A and beta-lactoglobulin at pH 8 and 40 degrees C, were determined by the digestion method. Thus, it was shown that digestion by proteases proceeds mainly via the unfolded state of proteins.     

Identification with monoclonal antibodies of virus-specific DNA-binding proteins in the nuclei of cells infected with three serotypes of Marek''s disease virus-related viruses.

Two groups of virus-specific polypeptides were identified in the nuclei of infected cells by cross-reacting monoclonal antibodies with three serotypes of Marek's disease virus. Of these, a 135,000-molecular-weight polypeptide common to all three serotypes was found to bind to both double-stranded and single-stranded DNAs.     

Purification of natural human interferon-gamma by antibody affinity chromatography: analysis of constituent protein species in the dimers

A simple procedure for purifying human interferon-gamma from leukocytes was established, based on monoclonal antibody affinity chromatography. The recovery of interferon activity was essentially quantitative, and the specific activity of the product was (4-12) x 10(7) international units/mg protein. SDS-polyacrylamide gel electrophoresis reproducibly revealed four components associated with interferon activity (and no other proteins): two major ones with molecular weights (MW) of 24,000-25,000 (25K) and 19,000-20,000 (20K), a minor one with MW 14,000-15,000 (15K) (these three bands were doublets), and a still less prominent one(s) with MV 40,000-48,000. Gel filtration in neutral solution indicated that all the 25K, 20K, and 15K species exist as oligomers, probably dimers. By means of experiments using a cleavable crosslinking reagent, the dimers were shown to comprise both homo-and heterodimers. Gel filtration in alkali (the condition used during purification) indicated that the molecules are largely in a monomeric state. Thus, the molecules once dissociated in alkali appear to reassociate at random upon neutralization; this process takes place without being accompanied by inactivation.     

Influence of inositol 1,4,5-trisphosphate and guanine nucleotides on intracellular calcium release within the N1E-115 neuronal cell line

The Ca2+ accumulating properties of a nonmitochondrial intracellular organelle within cultured N1E-115 neuroblastoma cells containing an (ATP + Mg2+)-dependent Ca2+ pump were recently described in detail (Gill, D. L., and Chueh, S. H. (1985) J. Biol. Chem. 260, 9289-9297). Using both saponin-permeabilized N1E-115 cells and microsomal membranes from cells, this report describes the effectiveness of both inositol 1,4,5-trisphosphate (IP3) and guanine nucleotides in mediating Ca2+ release from this internal organelle, believed to be endoplasmic reticulum. Using permeabilized N1E-115 cells, 2 microM IP3 effects rapid release (t1/2 less than 20 s) of approximately 40% of accumulated Ca2+ releasable with 5 microM A23187. Half-maximal Ca2+ release occurs with 0.5 microM IP3, and maximal release with 3 microM IP3. Using a frozen microsomal membrane fraction isolated from lysed cells, 2 microM IP3 rapidly releases (t1/2 less than 30 s) 10-20% of A23187-releasable Ca2+ accumulated within nonmitochondrial Ca2+-pumping vesicles, although only in the presence of 3% polyethylene glycol (PEG). 10 microM GTP, but not guanosine 5'-(beta, gamma-imido)triphosphate (GMPPNP), increases the extent of release in the presence of IP3. Importantly, however, GTP alone induces a substantial release of Ca2+ (up to 40% of releasable Ca2+) with a t1/2 value (60-90 s) slightly longer than that for IP3. The effects of IP3 and GTP are approximately additive, and both effects require 3% PEG. Half-maximal Ca2+ release occurs with 1 microM GTP, with maximal release at 3-5 microM GTP; 20 microM GMPPNP has no effect on release and only slightly inhibits 5 microM GTP; 20 microM GDP promotes full release, but only after a 90-s lag, and initially inhibits the action of 5 microM GTP. Using permeabilized N1E-115 cells, 5 microM GTP with 3% PEG releases greater than 50% of releasable Ca2+; without PEG, GTP still mediates approximately 30% release of Ca2+ from cells. Neither IP3, GTP, or both together (with or without PEG) effects release of Ca2+ accumulated within synaptic plasma membrane vesicles. The profound effectiveness of GTP on Ca2+ release has important implications for intracellular Ca2+ regulation and is probably related to Ca2+ release mediated by IP3.     

Purification and characterization of poly(ADP-ribose) glycohydrolase. Different modes of action on large and small poly(ADP-ribose)

Poly(ADP-ribose) glycohydrolase was purified approximately 74,000-fold to apparent homogeneity from calf thymus with a yield of 3.2%. The enzyme was a monomeric protein of Mr = 59,000, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The action of glycohydrolase on poly(ADP-ribose) was exoglycosidic in the direction of adenosine terminus----ribose terminus; radioactive ADP-ribose monomers were immediately produced from evenly labeled poly(ADP-ribose), but not from the polymer labeled selectively at the ribose terminus. The enzymatic degradation of large poly(ADP-ribose) (greater than 20 ADP-ribose residues) proceeded in a biphasic as well as bimodal manner. In the early and rapid phase, the enzyme degraded part of large polymers successively, leaving the remainder completely intact, and accumulated ADP-ribose monomers and small polymers of the size less than half of original polymers, indicating that the enzyme action was processive up to a certain extent. In the late and 20-fold slower phase, by contrast, the enzyme degraded the accumulated small polymers gradually and evenly, i.e. in a nonprocessive manner. The Km for large polymers was approximately 100-fold lower than that for small polymers. Similar rates and processivities were observed with large and small polymers bound to various proteins. These results suggested that the glycohydrolase may regulate differentially the levels of large and small poly(ADP-ribose) in the cell.