Separation of nuclei, cytosol and mitochondria

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Separation of nuclei, cytosol and mitochondria

To biochemically analyse the cell content,
some methods are employed to separate the nuclei, cytosol and mitochondria.
After isolating the nuclei, cytosol and mitochondria with centrifugation methods, assays are carried out to identify the 3 cellular portions.
To identify cytosol, the enzymatic activity of LDH is detected.
To identify mitochondria, the enzymatic activity of 5'-nucleotidase is detected.
To identify nuclei, the DNA content is detected.
The question are,
1.) how to detect the LDH activity?
2.) how to detect the 5'-nucleotidase?
3.) Ethidium Bromide can be used to bind to the DNA, and the fluoresence degree can be used to identify the DNA portion. But how does EtBr bind to the DNA?