Penicillium islandicum produced an inducible extracellular chitosanase when grown on chitosan. Large-scale production of the enzyme was obtained using R hizopus rhizopodijorrnis hyphae as substrate. Chitosanase was purified 3 8-fold to homogeneity by ammonium sulphate fractionation and sequential chromatography on DEAE-Biogel A, Biogel P,, and hydroxylapatite. Crude enzyme was unstable at 37 OC, but was stabilized by 1.0 mM-Ca2+. The pH optimum for activity was broad and dependent on the solubility of the chitosan substrate. Various physical and chemical properties of the purified enzyme were determined.Penicillium islandicum chitosanase cleaved chitosan in an endo-splitting manner with maximal activity on polymers of 30 to 60% acetylation. No activity was found on chitin (100 % acetylated chitosan) or trimers and tetramers of N-acetylglucosamine. The latter two oligomers and all small oligomers of glucosamine inhibited the activity of chitosanase on 30 % acetylated chitosan. The pentamer of N-acetylglucosamine and glucosamine oligomers were slowly cleaved by the enzyme. Analysis of the reaction products from 30% acetylated chitosan indicated that the major oligomeric product was a trimer; with 60% acetylated chitosan as substrate a dimer was also found. The new terminal reducing groups produced by chitosanase hydrolysis of 30 % acetylated chitosan were reduced by sodium b~ro [~H]hydride. The new end residues were found to be N-acetylglucosamine. The analyses strongly indicated that P. islandicum chitosanase cleaved chitosan between N-acetylglucosamine and glucosamine. Both residues were needed for cleavage, and polymers containing equal proportions of acetylated and non-acetylated sugars were optimal for chitosanase activity. The products of reaction depended on the degree of acetylation of the polymer.
Messenger RNA isolated from chicken pituitaries was used to construct a chicken pituitary cDNA library. A chicken growth hormone cDNA clone was isolated using 32P-labeled mammalian growth hormone cDNA probes. The amino acid sequence (derived from the DNA sequence) of the mature form of chicken growth hormone shows 77% homology with that of bovine growth hormone. The chicken growth hormone cDNA clone was used to generate a vector capable of producing chicken growth hormone in Escherichia coli. The recombinant E. coli-derived chicken growth hormone was similar to pituitary chicken growth hormone in several biochemical and immunological properties. The recombinant-derived hormone has been used to establish a sensitive radioimmunoassay for growth hormone determinations made from chicken sera. The chicken growth hormone gene has also been introduced into a retroviral vector capable of establishing productive infections of chicken cells both in in vitro and in vivo. The resulting infections are accompanied by the production of radioimmunoassay-detectable growth hormone. The concentrations of growth hormone in sera of Leghorn chickens infected with the recombinant retrovirus are three- to tenfold higher than in control animals.
The isolation of bacterially synthesized, recombinant-DNA-derived, bovine growth hormone (r-bGH) with native structure is described. The r-bGH is found in insoluble form, in a pellet fraction, after cell breakage and centrifugation. Cell envelope components (protein, lipid, endotoxin) and nucleic acids are selectively removed from the pellet fraction by an EDTA/lysozyme/deoxycholate extraction. We demonstrate that the r-bGH is largely reduced until solubilized using 6 M guanidine/HCl. Air oxidation is then carried out, in the presence of the guanidine/HCl. The oxidation results in a mixture of about one-third disulfide-linked oligomers and two-thirds oxidized monomer. The latter may include some incorrectly oxidized material, but appears to be mostly correctly oxidized. The oxidized monomer is isolated by gel filtration in the presence of guanidine/HCl. Subsequent guanidine/HCl removal leads to refolded, oxidized r-bGH. All steps in the procedure, in particular the oxidation and refolding steps, can be carried out at relatively high protein concentrations.
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