Which functional group is primarily involved in formaldehyde crosslinking of proteins?

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Multiple Choice

Which functional group is primarily involved in formaldehyde crosslinking of proteins?

Explanation:
The key player here is the primary amine group. In proteins, amino groups on lysine residues and at N-termini readily react with formaldehyde. The reaction begins when formaldehyde adds to an -NH2 to form a hydroxymethyl amine (N-CH2OH). This intermediate can then react with a second amino group to create a methylene crosslink (N-CH2-N), effectively linking two parts of the protein or neighboring proteins. This crosslinking helps preserve structure during fixation. Other groups, like hydroxyl (-OH), carboxyl (-COOH), or thiol (-SH) groups, don’t form the same stable crosslinks with formaldehyde under typical fixation conditions, so they’re not the primary sites for this process.

The key player here is the primary amine group. In proteins, amino groups on lysine residues and at N-termini readily react with formaldehyde. The reaction begins when formaldehyde adds to an -NH2 to form a hydroxymethyl amine (N-CH2OH). This intermediate can then react with a second amino group to create a methylene crosslink (N-CH2-N), effectively linking two parts of the protein or neighboring proteins. This crosslinking helps preserve structure during fixation.

Other groups, like hydroxyl (-OH), carboxyl (-COOH), or thiol (-SH) groups, don’t form the same stable crosslinks with formaldehyde under typical fixation conditions, so they’re not the primary sites for this process.

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