Question: What pair of modified amino acids is very common in collagen? 
 Options:  <1> 4-Hydroxy-proline and 5-Hydroxy-lysine. <2> Histamine and 5-Methyl-lysine. <3> Carboxyglutamate and 4-Hydroxy-proline. <4> S-Adenosyl-methionine and 5-Methyl-proline. <5> Methyl-Phenylalanine and Histamine.
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