Which organ catalyses hydrogen peroxide

Be careful using the sharp knife. An adult may need to help with this. Blend on high speed, pulsing when necessary, until the liver is smooth and no chunks are present. Be careful of the sharp blades in the blender. To the blended liver drop, add one drop of hydrogen peroxide.

You should see a lot of bubbles! What do you think the bubbles are made of? This shows that the liver enzyme catalase is working to start the chemical reaction that breaks down the hydrogen peroxide that would be harmful to the body into less dangerous compounds.

What is the color and consistency of this mixture? Put one drop of the mixture on a clean part of the large plate and add one drop of hydrogen peroxide to it.

Compared with the untreated blended liver, did more, less or about the same amount of bubbles form? Did they form more slowly, more quickly or at about the same rate? Did more, less or about the same amount of bubbles form? Cover the bowl and microwave it on high for 20 seconds. How does the blended liver look after heating? Remove a drop-size amount of the heated liver and put it on a clean part of the large plate.

Add one drop of hydrogen peroxide to it. Which condition s makes it work the worst? Why do you think this is so? For example, try freezing some blended liver or mixing it with salt and then test the enzyme's activity. Or you could try adding more than one teaspoon of vinegar or baking soda and then test the enzyme. Under which conditions does the enzyme work well, and under which ones does it work poorly?

One protein that is fun to digest using bromelain is gelatin, which is found in many puddings and gelatinous desserts. How do different conditions affect the ability of bromelain to digest proteins? If hemoglobin is present, the hydrogen peroxide decomposes to yield oxygen that in turn oxidizes the phenolphtalin to phenolphthalein.

Since the solution is basic, a pink colour develops indicating the presence of blood. The test is very sensitive, but is not specific for human blood. Animal blood will also yield a positive reaction as will oxidizing agents such as some metal ions.

The technique is to spray the suspect area with a solution of luminol and hydrogen peroxide. If blood is present, the peroxide will yield oxygen that then reacts with luminol to produce a blue glow. This reaction was first noted in by the German chemist H. Albrecht and was put into forensic practice in by forensic scientist Walter Specht.

Even dried and decomposed blood gives a positive reaction with the blue glow lasting for about 30 seconds per application. The glow can be documented with a photo but a fairly dark room is required for detection.

The reaction is so sensitive that it can reveal blood stains on fabrics even after they have been laundered. In one case, a pair of washed jeans with no visible stains gave a positive test with luminol on both knees. Neither the Kastle-Meyer test nor the luminol test can identify whose blood is involved, but once a stain has been determined to be blood, traces of DNA can be extracted and an identification carried out.

In the example of the jeans, DNA analysis was able to exclude the blood coming from the owner of the jeans. Luminol analysis does have drawbacks. Its chemiluminescence can also be triggered by a number of substances such as copper-containing compounds and bleaching agents. The proposed catalytic mechanism supports that catalase enzyme is never saturated with its substrate, H 2 O 2 , and that turnover of enzyme increases indefinitely as substrate concentration increases [ 2 ].

Apparently, catalases have been recognized with a rapid turnover rate and the maximum observed velocities ranging between 54, and , reactions per second [ 3 ].

The classical kinetic parameters, Vmax, kcat, and Km, cannot be directly applied to the observed data as catalases do not follow Michaelis-Menten kinetics except at very low substrate concentrations. However, at concentrations below mM, all small subunit size catalases show Michaelis-Menten-like dependence of velocity. At concentrations above — mM, most small subunit size catalases suffer inactivation.

Conversely, large subunit size catalases begin to suffer inhibition above 3 M hydrogen peroxide concentrations [ 1 , 3 ]. Their structure is composed of four domains Figure 2 [ 26 , 30 , 46 , 47 ]: An amino-terminal arm.

Schematic drawing of the polypeptide chain and elements of secondary structure in a S. This figure is taken from the report of Yuzugullu et al. The amino-terminal domain is an extended arm and is quite variable in length ranging from 53 residues in Proteus mirabilis catalase PMC to in HPII [ 30 , 47 ]. This domain is shown to constitute expanded intersubunit interactions, and residues from this region confer us to describe the heme pocket of a symmetry-associated subunit.

On the other hand, the second half corresponds to the NADP H -binding pocket in small subunit catalases. This part of the polypeptide chain is involved in different interdomain and intersubunit interactions especially with residues from the amino-terminal arm region from another subunit [ 30 , 47 ].

The possible role of this extra domain in PVC remains unknown [ 30 ]. The imidazole ring of distal histidine is placed almost parallel to the heme at a mean distance of about 3. The histidine and asparagine residues on the distal side of the heme make the environment strongly hydrophobic [ 30 ].

Despite possessing the same type of heme in active site, PVC and HPII differ in the presence of covalent bond between tyrosine and histidine residues. The limited accessibility to heme grouping catalases requires the presence of channels [ 30 ].

The heme of the enzyme is connected to the exterior surface by three channels, namely, the main channel, the lateral channel, and the central channel.

Among them, the main channel is placed perpendicular to the surface of the heme. The lateral channel approaches horizontal to the heme and the central one heading from the distal side [ 34 , 45 ]. The main channel is considered to be the primary route for substrate movement to the active site [ 1 , 3 ]. The role of aspartate has not been investigated in any catalase, but the presence of negatively charged side chain has been found to be critical for catalysis [ 45 ].

The lateral or minor channel approaches heme above and below the essential asparagine and emerges in the molecular surface at location corresponding to the NADP H -binding pocket in catalases that bind a cofactor Figure 4 [ 30 , 50 ].

The function of this channel remains unknown [ 34 ]. Molecular dynamics analysis indicates that water can exit the protein through this channel [ 4 ]. The main channel is a preferred route for substrate entry, but it might be too long and narrow for the release of reaction products water and molecular oxygen. As the central channel is mainly hydrophilic and leads to the central cavity that is contiguous to the bulk water, this could be a way out for O 2. However, substitutions of amino acid residues extending the major channel in large catalases might allow the exit of oxygen through the main channel.

In fact, oxygen preferentially exits through the main channel instead of central one in all catalases having b-type heme in the active site. Thus, the presence of minor channels might be an alternative mechanism for a fast release of products under the condition of high H 2 O 2 stress.

These results indicate that O 2 can exit the enzyme through different channels although the main exit in large catalases might be through the central channel and in small catalases through the major channel [ 34 , 51 ]. Many reports on catalase and phenol oxidase enzymes suggest that the activities may flap in some way that catalases exhibit additional oxidase activity and phenol oxidases present further catalase activity. This relationship can be explained by the release of H 2 O 2 due to polyphenol oxidation [ 52 ].

Hydrogen peroxide generation by phenol oxidation was also reported by Aoshima and Ayebe [ 53 ]. They observed high concentrations of H 2 O 2 in beverages like tea or coffee directly after opening caps as a result of oxygen.

Jolley et al. Garcia-Molina et al. In addition to this novel tyrosinase, a catalase-like process was found to have one isozyme of catechol oxidase from sweet potatoes Ipomoea batatas [ 57 ]. In literature, the first report on catalase known as a monofunctional enzyme but possessing secondary activity oxidase was introduced for mammalian catalase. This enzyme has been reported to present oxidase activity when hydrogen peroxide is absent or levels of H 2 O 2 are low.

As mentioned previously, the main function of catalase is the decomposition of hydrogen peroxide into water and oxygen catalytic activity. Moreover, it is known that catalases can oxidize low molecular weight alcohols in the presence of low concentrations of H 2 O 2 peroxidatic activity.

The peroxidase activity stems from the oxidation of alcohols by compound I through single-electron transfer. This oxidase reaction involves the interaction of catalase heme with a strong reducing agent like benzidine HB and molecular oxygen leading to the formation of a compound II-like intermediate. The subsequent electron transfer causes substrate oxidation and regeneration of resting enzyme.

An incomplete reaction may result in the formation of radical centered intermediates and the production of superoxide [ 14 ]. Later, catalase from the thermophilic fungus S. This enzyme, named as CATPO, is the first bifunctional catalase-phenol oxidase in the literature that is characterized in detail.