PubMed · 8753445
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K Murakami, K Okajima, H Okabe. 1995. [Catalase].. https://pubmed.ncbi.nlm.nih.gov/8753445/
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The reactions of the fungal enzymes Arthromyces ramosus peroxidase (ARP) and Phanerochaete chrysosporium lignin peroxidase (LiP) with hydrogen peroxide (H(2)O(2)) have been studied. Both enzymes exhibited catalase activity with hyperbolic H(2)O(2) concentration dependence (K(m) approximately 8-10 mm, k(cat) approximately 1-3 s(-1)). The catalase and peroxidase activities of LiP were inhibited within 10 min and those of ARP in 1 h. The inactivation constants were calculated using two independent methods; LiP, k(i) approximately 19 x 10(-3) s(-1); ARP, k(i) approximately 1.6 x 10(-3) s(-1). Compound III (oxyperoxidase) was detected as the majority species after the addition of H(2)O(2) to LiP or ARP, and its formation was accompanied by loss of enzyme activity. A reaction scheme is presented which rationalizes the turnover and inactivation of LiP and ARP with H(2)O(2). A similar model is applicable to horseradish peroxidase. The scheme links catalase and compound III forming catalytic pathways and inactivation at the level of the [compound I.H(2)O(2)] complex. Inactivation does not occur from compound III. All peroxidases studied to date are sensitive to inactivation by H(2)O(2), and it is suggested that the model will be generally applicable to peroxidases of the plant, fungal, and prokaryotic superfamily.
Hydroperoxidases (HP) are normally large haem-containing bifunctional enzymes capable of acting as both catalases and peroxidases. The C-terminal domain of HPI from Escherichia coli (KatG), extending from residue Tyr422 to Leu726, was found to be resistant to trypsin proteolysis. The segment of katG encoding this domain was cloned and overexpressed to produce a haemless protein that is soluble even at concentrations above 30 mg ml(-1). This protein shows a 25% sequence identity with cytochrome c peroxidase (CCP) from Saccharomyces cerevisae, despite lacking the characteristic catalytic and iron-binding residues. Crystals from this protein were grown in 0.6 M sodium citrate buffered to pH 7.5 with HEPES by the hanging-drop vapour-diffusion method at 293 K. These crystals diffracted beyond 2.0 A resolution and belong to space group P2(1)2(1)2(1), with unit-cell parameters a = 84.2, b = 98.7, c = 302.8 A. Three pseudo-origin peaks in the Patterson maps indicate an unusual packing compatible with the presence of three molecules in the crystal asymmetric unit and a solvent content of about 80% by volume.
A glucose-sensitive polymeric composite membrane was prepared based on our previously developed stimuli-responsive membrane system. Membranes were cast from a mixture of glucose oxidase (GOD), catalase, and poly(N-isopropylacrylamide-co-methacrylic acid) (poly(NIPAm/MAA)) nanoparticles dispersed in a solution of a hydrophobic polymer. High efficiency of enzyme immobilization was achieved with undetectable leakage. The bioactivity of the immobilized GOD, as measured by pH change of glucose solutions, was found to be equivalent to approximately 80% of that of the free GOD. The addition of catalase markedly increased the oxidation rate of glucose. However, an optimal unit ratio of GOD to catalase and optimal enzyme loading were observed. The rate of insulin permeation through the membrane was modulated by glucose concentration due to shrinking or swelling of the embedded pH-sensitive nanoparticles. The response of insulin permeability to the change in the glucose concentration could be detected within 5-15 min. The permeability of insulin increased more than 3-fold as the glucose concentration was raised from 50 to 200 mg/dl. The average insulin permeability at 400 mg/dl of glucose was 8-fold that at 50 mg/dl in a continuous test in saline and was 6-fold in a three-cycle discontinuous test in pH 7.4 buffer.