The thermal induced helix--beta transition of poly(N epsilon-methyl-L-lysine) and poly(N delta-ethyl-L-ornithine) in aqueous solution

Uncharged poly(N^ε-methyl-L -lysine) (PMLL) and its isomer, poly(N^δ-ethyl-L -ornithine) (PELO), in alkaline solution (pH ca. 12) undergo a helix-to-β transition upon mild heating at 50°C or higher in a manner similar to that of poly(L -lysine) (PLL). The rate of conversion follows the order: PMLL < PELO < PLL. The helix can be regenerated upon cooling near zero degrees, for instance, after more than 12 hr at 2°C. At concentrations less than 0.02% the β form is intramolecular, but at higher concentrations both intra- and intermolecular β forms are generated. Poly(N^δ-methyl-L -ornithine) (PMLO), an isomer of PLL, behaves like poly(L -ornithine); uncharged PMLO in alkaline solution is partially helical and becomes disordered at elevated temperatures.     

Protein polymorphism in a feral population of the pigeon Columba livia domestica

Sixteen enzymatic and non-enzymatic proteins of the pigeon Columba livia domestica were examined electrophoretically. These proteins were presumed to be under control by 22 loci. Of the 22 loci, 6 were defined as polymorphic and 15 as monomorphic. Another locus was variable, but the variation was not genetically interpretable. Average heterozygosity calculated over 21 loci was 0.075.     

Monodeiodination of thyroxine to 3, 5, 3'-triiodothyronine and to 3, 3', 5'-triiodothyronine in isolated dog renal cortical tubuli

Monodeiodination of T4 to T3 and rT3 in the intact cells of dog renal tubuli and glomeruli was investigated. The tubuli and glomeruli were obtained by a sieve method. T4 (2 micrograms/ml) was incubated in Tris-HCl buffer, pH 7.5, with renal cells (180 micrograms protein/ml) and 5 mM DTT for 1 h at 37 degrees C and the T3 and rT3 generated during incubation were measured by specific radioimmunoassays. In order of decreasing activity, dog renal cortical tubuli, cortical homogenate, glomeruli and medullary tubuli were capable of converting T4 to T3. Net rT3 production from T4 in cortical tubuli was also greater than that in cortical homogenate. The conversion of T4 to T3 and also to rT3 in cortical tubuli was enzymatic in nature, since the reactions showed dependence on time and protein concentration; instability to heating; temperature and pH optimum. The production of T3 and rT3 from T4 was maximum at pH 6.5 and at pH 9.5, respectively, indicating that two different enzymic systems, a 5- and a 5'-monodeiodinase, might be involved in the deiodination of the tyrosyl and the phenolic ring of T4 in dog kidney.     

Nucleotide sequence of the PR-1 gene of Nicotiana tabacum

A gene encoding one of the pathogenesis-related proteins, PR1a, and two related pseudogenes were isolated from Nicotiana tabacum. The cloned PR1a gene (pPR-gamma) and one of the pseudogenes (pPR-alpha) were sequenced and found to have similar structures. The sequence of pPR-gamma was quite similar to that of the cDNA clone of PR1a. The plasmid pPR-gamma did not contain an intron and had a typical promoter sequence in the 5'-flanking region.     

Human skeletal muscle contains two major aminopeptidases: an anion-activated aminopeptidase B and an aminopeptidase M-like enzyme

Two major aminopeptidases, an aminopeptidase B and an aminopeptidase M-like enzyme, were purified from human skeletal muscle by DEAE-cellulose, HPLC gel filtration, and hydroxyapatite column chromatographies. The purified aminopeptidase B exhibits a molecular weight of 76,000 under both native and denaturing conditions. The activity of the aminopeptidase B is regulated by C1 ions and other anions in vitro. On the other hand, the aminopeptidase M-like enzyme is a monomeric protein having a molecular weight of 96,000. It is capable of significantly cleaving Phe-, Leu-, Arg-, and Ala-aminoacyl bonds in the presence of 2-mercaptoethanol. The pH optima for both enzymes are around 7.0, and bestatin is an effective inhibitor of both enzymes.     

Prostaglandin-E2-induced activation of adenosine 3'-5' cyclic monophosphate-dependent protein kinases of a murine macrophage-like cell line (P388D1)

Changes in the activities of adenosine 3',5'-cyclic monophosphate (cAMP)-dependent protein kinases in response to prostaglandin (PG)E2-induced elevation of intracellular cAMP level were investigated with a murine macrophage-like cell line, P388D1. Photoaffinity labeling with 8-azido-[32P]cAMP showed that untreated P388D1 cells possess two types of cAMP-binding proteins of m.w. 49,000 and 52,000, respectively, in the cytosol fraction in a ration of 1:8. They must represent regulatory subunits (RI and RII, respectively) of cAMP-dependent protein kinases, because affinity chromatography on a column of omega-aminohexyl-agarose of the cytosol fraction clearly separated two fractions that exhibited the enzymatic activities and cAMP-binding activities. Photoaffinity labeling of these fractions with 8-azido-[32P]cAMP confirmed the separation of two types of isoenzymes, because each cAMP-dependent protein kinase active fraction was associated with only one type of regulatory subunit. The exposure of P388D1 cells to exogenously added PGE2 (1 microM) caused about 7.5-fold increase in the intracellular cAMP level within 30 sec. The cAMP level then sharply dropped to about 100 pmol/10(7) cells, remained at this level for about 20 min, and then gradually increased to 200 pmol/10(7) (about fivefold over the control). The enzyme assay of the cytosol demonstrated that the activation of cAMP-dependent protein kinases closely follows the kinetics of the intracellular cAMP level. The activation of the enzyme was specific for PGE2 and was not triggered by 1 microM PGF2 alpha or PGD2 which have been shown to be unable to activate adenylate cyclase of P388D1 cells. The PGE2-induced increase in the intracellular cAMP level appeared to activate preferentially the type I isoenzyme, inasmuch as the enzymatic activity of this type separated by the affinity chromatography of the cytosol of PGE2-exposed cells was lower in the presence than in the absence of cAMP, whereas the type II enzyme activity remained responsive to exogenously added cAMP.     

Glutamine Synthetase of the Human Brain: Purification and Characterization

Glutamine synthetase (GS) isolated from human brain formed a single band on sodium dodecyl sulfate-polyacrylamide gel with a molecular weight of 44,000. The enzyme had a specific activity of 179.2 U/mg protein when assayed by measuring the rate of the formation of gamma-glutamylhydroxamate using hydroxylamine as a substrate. In the presence of manganese ions, the relative activity of human brain GS was much lower than that of the sheep brain enzyme. The suppression of activity by increasing the ADP concentration, however, was less marked in the human enzyme than that in the sheep enzyme. Antibodies were raised in rabbits against the purified enzyme. The double-immunodiffusion technique disclosed cross-reactivities among GSs isolated from human, sheep, and rat brains, but the enzymes were not immunologically identical. Immunohistochemically, GS was localized in the cytoplasm of astrocytes in the human and rat brains and in pericentral hepatocytes of the liver.