Protein degradation systems

Rehner This suggestion is not sufficient to explain your results with cycloheximide. If cycloheximide is added, the inhibitor should already have been made. In this case the timing can only work if a protein degradation system is switched on on time in the absence of protein synthesis. 

Hofmann, K. and Falquet, L. A ubiquitin-interacting motif conserved in components of the proteasomal and lysosomal protein degradation systems. Trends Biochem Sci 2001, 26, 347-50. 

Another nonlysosomal protein degradative system is dependent on calcium ions. They combine with specific protein residues in close proximity to each other proline, glutamate, serine, and threonine (PEST sequences). It is believed that a calcium-requiring proteinase (a metalloenzyme) recognizes the calcium and combines with it, thus achieving an active status, and then hydrolyzes the protein in the vicinity of the PEST sequence. 

Transglutaminase 1 + and 2 Protein degradation systems Ubiquitin-proteasome system NK NK NK [42]... 

Brief History of Protein Degradation and the Ubiquitin System... 

The functional proteins in the cell have to be protected in order to prevent premature degradation. Some of the intracellularly active proteolytic enzymes are therefore enclosed in lysosomes (see p. 234). The proteinases that act there are also known as cathepsins. Another carefully regulated system for protein degradation is located in the cytoplasm. This consists of large protein complexes (mass 2 10 Da), the proteasomes. Proteasomes contain a barrel-shaped core consisting of 28 subunits that has a sedimentation coef cient (see p. 200) of 20 S. Proteolytic activity (shown here by the scissors) is localized in the interior of the 20-S core and is therefore protected. The openings in the barrel are sealed by 19-S particles with a complex structure that control access to the core. 

There is also a corresponding circulation system for the amino acid alanine. The alanine cycle in the liver not only provides alanine as a precursor for gluconeogenesis, but also transports to the liver the amino nitrogen arising in muscles during protein degradation. In the liver, it is incorporated into urea for excretion. 

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