**Question:** Post translational modification of lysine and proline is by

A. Protein Kinase C
B. Protein Phosphatase
C. Protein Tyrosine Kinase
D. Glycosylase

**Core Concept:** Post-translational modifications (PTMs) are chemical reactions that occur after a protein is translated from its mRNA sequence. They play a crucial role in shaping protein function, localization, and interactions with other molecules. The modifications include phosphorylation, acetylation, ubiquitination, and glycosylation.

**Why the Correct Answer is Right:** Lysine and proline are amino acids involved in various biological processes, including protein structure, stability, and function. The correct answer, D (Glycosylase), refers to a group of enzymes that remove or modify glycosidic bonds in proteins, peptides, or nucleic acids. Glycosylation is one type of post-translational modification involving the attachment of carbohydrates (sugars) to proteins, regulating their stability, folding, and interactions with other molecules.

**Why Each Wrong Option is Incorrect:**

A (Protein Kinase C) is a kinase that phosphorylates serine, threonine, and tyrosine residues in proteins, regulating various cellular processes and signaling pathways. It is not involved in the modification of lysine or proline.

B (Protein Phosphatase) is an enzyme that catalyzes the removal of phosphate groups from proteins, reversing the effects of protein kinases. Protein phosphatases are involved in the regulation of protein function and localization, but they do not modify lysine or proline residues.

C (Protein Tyrosine Kinase) is a group of enzymes that phosphorylate tyrosine residues in proteins, regulating cellular processes and signaling pathways. Protein tyrosine kinases are distinct from lysine and proline kinases, and thus, they are incorrect for the given question.

**Clinical Pearl:** Post-translational modifications are essential for a deep understanding of protein function, localization, and interactions. Identifying the correct modifications for specific amino acids can help in understanding diseases and therapeutic strategies targeting these modifications. For example, targeting lysine acetylation in cancer can lead to protein deacetylation, which could potentially inhibit tumor growth and progression.