Degradation of Proteins (2018) – Faisal Biochemist

Degradation of Proteins
  • Caused by Proteases.
  • Lysosomal Degradation of glycoproteins.
  • Ubiquitim Proteasome Degradation of Proteins.

Before we start, please You must know about:

History of DNA As Heredity Material 

Chemical and Physical Properties of Nucleic Acid


Present in Intestinal Track. 3 types of Proteases are:

 1) Endoproteases:

  • Trypsin:- Clearage at C-terminal of lys ad argimine e.g Asp à Lys à
  • Chymotrypin:- Cleavage at C-Terminal of aromatic acids (Hydrophobic resides).

2) Exopeptidases:

  • Aminopeptidase:- Clearage at N-terminus.
  • Carboxy Peptidases:- Cleavage at C-Terminus.

3) Peptidases:

  • Cleave large polypeptides to small peptidases.

Lysosomal degradation of Glycoproteins:

Proteins attach with carbohydrates Oligosaccharides Asn proteins.


  • Neuraminidase:- It attacks on acuity, the Neuraminic acid of Oligosaccharides chain deficiency of this enzyme results in sialidosis. They have mental disorder eye abnormalities, facial deformation.
  • B-Galactosidase:- It attacks on B-Galactose. Deficiency of this enzyme leads to GM1 Gangliosidosis, MR (Mental Retarded) deformities other symptoms.
  • Acetyl – Glucosaminidase:- It attacks on acetyl Glucosamine. Deficiency of this enzyme leads to tay sach/sand hoff. It causes mentally retarded bone deformities.
  • α- Mannosidase:- It attacks on α Mannose. It’s deficiency leads to α-Mannosidosis. It causes mental retarded.
  • β- Mannosidase:- It attacks on β-mannose. It’s deficiency leads to β-Mannosidosis. It causes mental retarded.
  • Hexosaminidase:- It attacks on Acetate chitobiose (Present in Dog)… It is absent in human and rat. Instead of hexosaminidase humans and rat have chitobiose,.
  • Chitobiase:- It attacks on Acetyl chitobiose. It’s deficiency causes no disorder present in human and rat.
  • Fucosidase:- It attacks on fucose. It’s deficiency leads to fucosidosis. It causes mental retarded, heart muscles weaknesses.

The enzyme which attacks on Asn:

We have only 1 enzyme that attacks on Asn.

Glycosperginase:- It attacks Asn. It’s deficiency leads to Aspertylucosiminurla. Patients have metal retardation, severe diarrhea.

The enzyme which degrades Protein Part:

Cathepsins:- (A,B,C,D,H,L) 6 type of cathepsins degrade protein part. Active in the lysosome.

Ubiquitim Proteasome Degradation of Proteins:

Proteins which are degraded in the proteasome, firstly they are tagged with ubiquitin protein and they move toward proteasome for degradation.

Ubiquitin:- is a small protein of 8.5 xDa containing only 76 amino acids plays role in tagging or linking.

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