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Background• Enzyme name catalaseimportant enzyme in protecting the cell from oxidative damage by reactive oxygen species (ROS).• Substrate name hydrogen peroxide• Enzyme action breakdown of toxic H2O2 producing
oxygen gas and water
catalase
• 2H2O2 2H2O + O2
• Hydrogen peroxide produce due to the aerobic respiration of the cells and have to be breakdown to prevent it’s toxic action on DNA and cell membrane
Background• When hydrogen peroxide is added to a colony of catalase-producing
bacteria, it is broken down and the oxygen that is produced can be seen as bubbles .
• By catalase test we can distinguish between:– G (+ve) cocci : Staphylococcus positive where Streptococcus is catalase negative
– G (+ve) bacilli : Bacillus is catalase positive whereas Clostridium is catalase negative
– All enterobactrieacae (a gram negative bacilli) are catalse positive
– Lesteria monocytogenes ( a gram positive bacilli) are catalase positive
PROCEDURE a. Place a small amount of growth from culture
onto a clean microscope slide. If using colonies from a blood agar plate, be very careful not to scrape up any of the blood agar— blood cells are catalase positive and any contaminating agar could give a false positive.
b. Add a few drops of H2O2 onto the smear. If needed, mix with a toothpick. DO NOT use a metal loop or needle with H2O2; it will give a false positive and degrade the metal.
Interpretation
c. +ve result rapid evolution of O2 as evidenced by bubbling.
d. –ve result no bubbles or only a few scattered bubbles.
To Know• Catalase is usually located in a cellular, bipolar
environment organelle called the peroxisome• Louis Jacques Thénard, who discovered H2O2 (
hydrogen peroxide)• Oscar Loew was the first to give it the name catalase• Human catalase works at an optimum temperature
of 45 °C• pH between 6.8 and 7.5• one catalase molecule can convert approximately 5
million molecules[2] of hydrogen peroxide to water and oxygen each second