Lab 17: Enzymes of Respiration

Catalase Test 

-tests for enzyme catalase which breaks down 

hydrogen peroxide (H2O2) into water and oxygen

-medium= hydrogen peroxide substrate 

-Positive test= bubbles of O2

Oxidase Test 

-tests for enzyme cytochrome c oxidase which is the last component of the electron transport chain in aerobic and some facultative organisms 

-cytochrome c oxidase accepts electrons from cytochrome c (oxidizing it) and donates electrons to oxygen, reducing it into water

medium=BBL DrySlide oxidase Slide w/ reagent 

positive test= purple spot (by ~20sec)

negative= no change

Nitrate Reduction Test 

tests for the ability of an organism to reduce Nitrate (NO3-) to Nitrite (NO2-) using nitrate reductate

also tests for ability to do denitrification= reduce nitrate (NO3-) to Nitrite (NO2-) and eventually reducing it enough to Nitrogen Gas (N2)  using various enzymes 

* note- when reading these tests we start with N2 gas, then Nitrite, then Nitrate

Growth Medium= nitrate broth

Positive Test for N2= bubble

 Negative test for N2= no bubble-and Nitrite test is performed 

Nitrite (NO2-) test

growth medium= nitrate broth

reagents= sulfuric acid (H2SO4) and Tromdorff's reagent (TDR) 

Positive Test= immediate color change to brown/purple -seen on 1st row #6 and #8

Negative Test= no color change and Nitrate Test is performed

Nitrate (NO3-) test

growth medium= nitrate broth

reagents= sulfuric acid (H2SO4), Tromdorff's reagent (TDR) and Zinc

- zinc causes nitrate to be reduced to nitrite 

Positive Nitrate test= immediate change in color to purple/brown 

-seen in #5 second row