Lysosomes are membrane-bound organelles found in eukaryotic cells that function as the cell's primary site for the degradation and turnover of proteins and other macromolecules. The enzymes involved in this process are collectively referred to as lysosomal enzymes or hydrolases. These enzymes are responsible for breaking down various substrates, including proteins, lipids, carbohydrates, and nucleic acids. The specific enzymes involved in protein degradation in lysosomes include:1. Cathepsins: Cathepsins are a group of proteolytic enzymes that play a crucial role in lysosomal protein degradation. They are classified into three major types based on their catalytic mechanism: cysteine cathepsins e.g., cathepsin B, C, H, L, and S , aspartic cathepsins e.g., cathepsin D and E , and serine cathepsins e.g., cathepsin G and A . Cathepsins cleave peptide bonds in proteins, leading to their degradation into smaller peptides and amino acids.Mechanism of action: Cathepsins use a catalytic triad or dyad of amino acid residues to hydrolyze peptide bonds in proteins. For example, cysteine cathepsins utilize a catalytic triad consisting of a cysteine, histidine, and asparagine residue, while aspartic cathepsins use a catalytic dyad of two aspartic acid residues.2. Peptidases: In addition to cathepsins, lysosomes also contain various peptidases, such as dipeptidyl peptidase I also known as cathepsin C , which further degrade the peptides generated by cathepsins into individual amino acids or smaller peptides.Mechanism of action: Peptidases cleave peptide bonds at specific sites within the peptide chain, depending on their substrate specificity. This process ultimately generates free amino acids or smaller peptides that can be transported out of the lysosome and reused by the cell.3. Proteasomes: Although not strictly lysosomal enzymes, proteasomes are another essential component of the cellular protein degradation machinery. They are large, multi-subunit complexes that degrade proteins tagged with ubiquitin, a small protein that serves as a signal for proteasomal degradation. Proteasomes are primarily found in the cytoplasm and nucleus, but they can also be associated with lysosomes in certain cell types and under specific conditions.Mechanism of action: Proteasomes recognize and bind to ubiquitinated proteins, unfolding them and threading them through a central catalytic chamber. Within this chamber, proteasome-associated proteases cleave the protein into smaller peptides, which are then released and further degraded by other peptidases.In summary, the degradation and turnover of proteins in lysosomes involve the concerted action of various enzymes, primarily cathepsins and peptidases. These enzymes hydrolyze peptide bonds in proteins and peptides, ultimately generating free amino acids or smaller peptides that can be reused by the cell.