Xanthine oxidase,an indicator of secretory differentiation in mammary cells

Elevated levels of xanthine oxidase were found in (1) lactating mouse mammary glands, compared with virgin and midpregnant glands; and (2) primary mouse mammary cells cultured on floating collagen gels, compared with non-secretory cells on attached gels. In primary culture, increase in xanthine oxidase activity above a basal level coincided with secretory activity as measured by casein production; intracellular levels of casein and xanthine oxidase showed a high degree of correspondence. It is suggested that xanthine oxidase levels can be used as an indicator of in vivo and in vitro secretory differentiation in mammary epithelial cells.     

Biosynthesis of endothelium-derived relaxing factor: a cytosolic enzyme in porcine aortic endothelial cells Ca2+-dependently converts L-arginine into an activator of soluble guanylyl cyclase

In the presence of porcine aortic endothelial cytosol, soluble guanylyl cyclase purified from bovine lung was activated by L-arginine up to 2.5-fold, with an EC50 of about 6 microM. This activation was dependent on NADPH and Ca2+. The EC50 for Ca2+ was about 60 nM. No effect of L-arginine on guanylyl cyclase was observed when the cytosolic proteins were heat-denaturated. The effect of L-arginine was inhibited by NG-monomethyl-L-arginine and hemoglobin. These results indicate that endothelial cells contain a cytosolic enzyme which is directly or indirectly regulated by Ca2+ and converts L-arginine into a compound which in stimulating soluble guanylyl cyclase behaves similar to endothelium-derived relaxing factor.     

Susceptibility of autologous target cells to lysis by lymphokine-activated effectors from interferon-α-treated chronic myelogenous leukaemia patients

Summary Chronic myelogenous leukemia (CML) patients in chronic phase display compromised lymphokine-activated killer (LAK) cell induction, which is partly restored after therapy with interferon . However, the relative resistance of the leukemic cells from these patients to autologous or allogeneic LAK lysis is not affected by this treatment. In an attempt to render CML cells more susceptible to lysis or cytostasis, they were precultured in serum-free medium with or without recombinant growth factors. In eight patients studied, interleukin-3 (IL-3) significantly enhanced the spontaneous short-term (6-day) proliferation of CML cells, with retention of ability to form colonies in methylcellulose. Culture in either medium alone or IL-3 led to a significant enrichment of CD14⁺ and CD33⁺ cells but to a reduction in CD34⁺ cells. In contrast, culture of the same cells in IL-2 (to generate autologous LAK activity) resulted in a loss of CD14⁺ and CD33⁺ as well as CD34⁺ cells but in a significant increase in CD3⁺ and CD56⁺ cells. Despite similarities in their phenotypes, IL-3 cultured cells but not those cultured in medium alone acquired susceptibility to lysis by the IL-2-cultured autologous LAK cells. These results may have significance for the design of novel combination immunotherapy in CML.This work was supported in part by the Deutsche Forschungsgemeinschaft (SFB 120)     

Bioconversion of 3-chlorobenzoate to 2-chloromuconate controlled by on line HPLC

Summary Strain RD330 a transposon mutant of Alcaligenes eutrophus JMP134 was considered to be dienelactone hydrolase defective (Don et al. 1985). During a bioconversion experiment with 3CB (3-chlorobenzoate) 2CMA (2-chloro-cis,cis-muconate) was accumulated by RD330 with an overall amount of 31%, but no dienelactone could be detected. Enzyme tests revealed that both enzymes 2CMA-cycloisomerase and dienelactone-hydrolase were induced at low levels in RD330 by 3CB and its metabolites.The control of 3CB addition during the bioconversion experiment was performed by on line HPLC (high pressure liquid chromatography).     

Association of thrombospondin of endothelial cells with other matrix proteins and cell attachment sites and migration tracks

Different biochemical and cytochemical techniques were applied to characterize the sites of localization of thrombospondin in cultured endothelial cells. The results obtained by [35S]methionine labeling, immunoblotting, immunoprecipitation, fluorescence microscopy, ultracytochemistry, immunogold labeling, and silver enhancement experiments revealed that thrombospondin secreted by endothelial cells is structurally organized together with proteoheparan sulfate in spherical granules at the cell surface. These granules are about 100 to 300 nm in size. Heparin or enzymatic degradation with heparitinase, but not with ABC lyase, release thrombospondin from the cell surface. Fibronectin is expressed in the extracellular matrix of endothelial cells in a fibrillar organization, clearly distinct from the punctate pattern of thrombospondin on the cell surface. Furthermore, secreted thrombospondin is highly enriched together with fibronectin and proteoheparan sulfate in cell attachment sites and in cell migration tracks. In cell migration tracks proteoheparan sulfate more clearly resembles the fibrillar distribution pattern of fibronectin, whereas thrombospondin reveals a rather monodisperse pattern. The obtained data suggest preferential sites of interaction between thrombospondin and heparan sulfate proteoglycans on the cell surface and a participation of thrombospondin in cell adhesion and cell migration.     

Chemical identification of cysteine as palmitoylation site in a transmembrane protein (Semliki Forest virus E1)

The palmitoylation site of the membrane glycoprotein E1 of Semliki Forest virus (SFV) has been identified by chemical analysis of an acylpeptide. 3H-Palmitoylated E1 isolated from SFV grown in baby hamster kidney cells was digested with chymotrypsin and the resulting peptides subjected to high performance liquid chromatography on a wide-pore column. The 3H-acylated peptide fraction peaked at above 60% 2-propanol in the eluent, indicating its hydrophobic character. Polyacrylamide gel electrophoresis analysis revealed a molecular weight of about Mr = 6000 for the radiolabeled peptide. Manual sequencing of this material by the 4-N,N'-dimethylaminoazobenzene-4'-isothiocyanate/phenylisothiocyanate procedure on solid phase revealed the amino-terminal sequence Ala-Ala-Ser-His-Ser-Asn-Val-Val-Phe-Pro. The same peptide also labels with [35S]cysteine. Comparison with the deduced amino acid sequence of E1 revealed that the palmitoylated peptide contains at least 43 amino acid residues, and thus includes the membrane spanning region down to the only cysteine residue five positions up from the carboxyl terminus of E1. Since [3H]palmitic acid was cleaved from E1 with thiol reagents, and since the peptide labels with [14C]iodoacetamide only after the release of fatty acids by hydroxylamine treatment, cysteine in position 433 represents the palmitoylation site in SFV E1.     

On the mechanism of formation of N-acetyldopamine quinone methide in insect cuticle

The mechanism of formation of quinone methide from the sclerotizing precursor N-acetyldopamine (NADA) was studied using three different cuticular enzyme systems viz. Sarcophaga bullata larval cuticle, Manduca sexta pharate pupae, and Periplaneta americana presclerotized adult cuticle. All three cuticular samples readily oxidized NADA. During the enzyme-catalyzed oxidation, the majority of NADA oxidized became bound covalently to the cuticle through the side chain with the retention of o-diphenolic function, while a minor amount was recovered as N-acetylnorepinephrine (NANE). Cuticle treated with NADA readily released 2-hydroxy-3′,4′-dihydroxyacetophenone on mild acid hydrolysis confirming the operation of quinone methide sclerotization. Attempts to demonstrate the direct formation of NADA-quinone methide by trapping experiments with N-acetylcysteine surprisingly yielded NADA-quinone-N-acetylcysteine adduct rather than the expected NADA-quinone methide-N-acetylcysteine adduct. These results are indicative of NADA oxidation to NADA-quinone and its subsequent isomerization to NADA-quinone methide. Accordingly, all three cuticular samples exhibited the presence of an isomerase, which catalyzed the conversion of NADA-quinone to NADA-quinone methide as evidenced by the formation of NANE—the water adduct of quinone methide. Thus, in association with phenoloxidase, newly discovered quinone methide isomerase seems to generate quinone methides and provide them for quinone methide sclerotization.