"the tertiary structure of the human enzyme called lysozyme is stabilized by ionic bonds between the r-groups (side chains) of amino acid subunits. which amino acid has an r-group that could form an ionic bond with the r-group of lysine? "

The tertiary structure of the proteins  is a three-dimensional structure. The polypeptides are arranged in a three-dimensional structure, which primarily arises because of the interaction between the side chains (R group) of the amino acids making up the protein.

The aspartic acid is a charged protein which is capable of forming the salt bridges. It can form ionic bonds with the R group of the other proteins. Hence, it can form ionic bond with the side chain of  the amino acid lysine.

Hence, the answer is aspartic acid.

a. 35°c

b. 25°c

c. 10°c

d. 40°c