Properties Of Phenoloxidase Research Articles

Properties of phenoloxidase from haemocytes of Scylla tranquebarica

The presence of phenoloxidase (PO) activity in the haemocytes of Scylla tranquebarica was electrophoretically and spectrophotometrically studied. Majority of the enzyme was located as proenzyme, prophenoloxidase (proPO) in the haemocytes. The enzyme prefers L-dihydroxyphenylalanine (L-dopa) as its substrate than phenol and is optimally active at pH 8.0. Besides trypsin, the proPO was also activated by both Gram positive and Gram negative microbes in vitro while, chemicals such as sodium azide, thiourea and EDTA significantly inhibited the enzyme expression. The protein needs considerable levels of divalent cations like calcium (20 mM as CaCl2) or magnesium (20–50 mM as MgCl2) for its activity. The gel filtration chromatography of haemocyte lysate supernatant showed a single major peak of protein having PO activity. Electrophoresis of purified PO by native PAGE revealed a single prominent band of approximately 167.2 kDa which was further resolved to three bands having molecular mass of approximately 77.1, 56.9 and 30.2 kDa respectively, on SDS-PAGE.

Purification and properties of phenoloxidase from spinach leaves.

A phenoloxidase from spinach leaves was extensively purified to homogeneity. The molecular weight of the purified enzyme was 150,000 by gel filtration, and 40,000 by SDS-polyacrylamide gel electrophoresis. The enzyme contained 2 atoms of copper per 150,000 of molecular weight. The optimum pH of the enzyme action is near 6.5. The enzyme lacks cresolase activity. Km and k0 were measured for some 4-substituted catechols and oxygen. Log k0 values for catechols substituted in position 4 by -N02, -CHO, -CH3, -COOH, or -CH2CH2COOH were confirmed to fit Hammett relationships (ρ-Values for a and am are - 3.652 and — 4.007, respectively), but not for log Km values. Log(k0/Km) values for the same substrates were confirmed to have this relationship, but protocatechuic and hydrocaffeic acids deviated from this linearity.

O-Diphenoloxidase of Mycobacterium leprae separated from infecected armadillo tissues.

We reported earlier the occurrence of a unique o-diphenoloxidase in Mycobacterium leprae recovered from lepromatous human tissues. No other source of M. leprae fro biochemical studies was available at the time. In the present report, properties of phenoloxidase in M. leprae separated from infected armadillo tissues are presented. The results show that the o-diphenoloxidase remains unaltered in the passage of the bacilli from the human to the the animal host, indicating that the enzyme is an intrinsic characteristic of the leprosy bacteria.

Properties of phenoloxidase in Mycobacterium leprae.

Mycobacterium leprae separated from infected human tissues, oxidizes 3,4-dihydroxyphenylalanine (dopa) and a few other phenolic compounds1–3. This property is not shown by several other mycobacteria1,2,4. Phenoloxidase occurs in vertebrate melanocytes and is widely distributed in the plant kingdom5. (E.C. 1.10.3.1, o-diphenol: oxygen oxidoreductase). For a large number of substrates the phenoloxidase of the leprosy bacilli is similar to the enzyme from plant sources, and distinct from mammalian phenolase, which has a limited substrate specificity6. When the reaction products were compared, another distinguishing feature of the M. leprae enzyme became evident and this is reported here.