Protein biosynthesis, post-translational

Carnitine acts catalytically and might be considered to be a cofactor of carnitine fatty acyltransferase. Unlike most cofactors, however, carnitine is not a vitamin and is not derived from a vitamin. Generally, all of the carnitine needed by the body can be S5mthesized by the body. The biosynthesis of carnitine begins in an unusual manner. The starting material, the lysine residues of a variety of proteins, undergo post-translational methylations, as shown in Figure 4.55. The methyl donor is S-adenosylmethionine. Trimethyllysine, liberated from the protein by intracellular hydrolysis, is hydroxylated and then converted to carnitine in three... 

Biosynthesis. The biosynthesis of neuropeptides is much more complex and involves the multistep process of transcription of specific mRNA from specific genes, formation of a high molecular weight protein product by translation, post-translational processing of the protein precursor to allow for... 

Clearly, the control of gene expression at the transcriptional level is a key regulatory mechanism controlling carotenogenesis in vivo. However, post-transcriptional regulation of carotenoid biosynthesis enzymes has been found in chromoplasts of the daffodil. The enzymes phytoene synthase (PSY) and phytoene desaturase (PDS) are inactive in the soluble fraction of the plastid, but are active when membrane-bound (Al-Babili et al, 1996 Schledz et al, 1996). The presence of inactive proteins indicates that a post-translational regulation mechanism is present and is linked to the redox state of the membrane-bound electron acceptors. In addition, substrate specificity of the P- and e-lycopene cyclases may control the proportions of the p, P and P, e carotenoids in plants (Cunningham et al, 1996). 

This interconnected network of membrane vesicles is divided into two distinct parts. The rough endoplasmic reticulum (RER), which is studded with ribosomes, is the site of membrane and secretory protein biosynthesis and their post-translational modification. The smooth endoplasmic reticulum (SER) is involved in phospholipid biosynthesis and in the detoxification of toxic compounds. 

Steinee, D. F. (2002). The prohormone convertases and precursor processing in protein biosynthesis. In Dalbey, R. E., Sigman, D. S. (Eds.), The enzymes co-and post-translational proteolysis of proteins, Vol. XXII. Academic, San Diego. 

Eisenhaber B, Maurer-Stroh S, Novatchkova M, Schneider G, Eisen-haber E. Enzymes and auxiliary factors for GPI lipid anchor biosynthesis and post-translational transfer to proteins. BioEssays 2003 25 367-385. 

Fig 12.7 Overview of Protein biosynthesis and Post translational modifications. Translational Inhibitors Antibiotics... 

Diversity of monomers The biosynthesis of natural proteins utilizes 20 different monomeric units, and chemical and enzymatic post-translational modifications provide further diversity of sequence. As discussed in Chapter 4 and noted below, the availability of 20 different monomers results in an inordinate number of different protein sequences, even for a small 100 residue protein, that is, 10 . 

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