Catabolic activator protein

Comparison of the model-derived DIFF with the experimentally evaluated DIFF show that protein routing can be described in terms of the amount of protein synthesized from catabolic activity that is, in general it is around 20% of the mean carbon flux of the diet. A simple explanation why dp > dw is also proposed. 

Thioesters play a paramount biochemical role in the metabolism of fatty acids and lipids. Indeed, fatty acyl-coenzyme A thioesters are pivotal in fatty acid anabolism and catabolism, in protein acylation, and in the synthesis of triacylglycerols, phospholipids and cholesterol esters [145], It is in these reactions that the peculiar reactivity of thioesters is of such significance. Many hydrolases, and mainly mitochondrial thiolester hydrolases (EC 3.1.2), are able to cleave thioesters. In addition, cholinesterases and carboxylesterases show some activity, but this is not a constant property of these enzymes since, for example, carboxylesterases from human monocytes were found to be inactive toward some endogenous thioesters [35] [146], In contrast, allococaine benzoyl thioester was found to be a good substrate of pig liver esterase, human and mouse butyrylcholinesterase, and mouse acetylcholinesterase [147],... 

Another example of positive regulation by CAP is provided by the seven proteins required for uptake of maltose and its catabolism by E. coli. These are encoded in two operons that are controlled as a single regu-lon. An apo-activator protein becomes an activator when it binds maltose.137138... 

Increased lipoprotein levels are seen in diabetes mellitus but not in starvation. Glucocorticoids have a protein catabolic activity in all tissues except liver. There, glucocorticoids stimulate protein synthesis. 

Because of the catabolism of proteins to (mostly) endogenous amino acids, classical biotransformation studies as performed for small molecules are not needed. Additionally, limitations of current analytical methods to detect and distinguish metabolites and the putative lack of pharmacological or toxicological activity of the metabolites, remain obstacles. Similarly mass balance studies... 

The detection of PI in bacterial and archaeal systems implies that PI synthase, which is an integral membrane protein, is present. Once PI is available, kinases could add phosphates to generate various phosphoinositides, although to date this chemistry has only been demonstrated to occur in eukaryotes. Bacterial catabolic activities specific to PI have also been identified. In most cases these are secreted soluble proteins that can cleave PI and in some cases GPI-anchored... 

Furst W, Sandhoff K. Activator proteins and topology of lysosomal sphingolipid catabolism. Biochim. Biophys. Acta 1992 1126 1-16. 

All the DNA-binding proteins discussed thus far function by inhibiting transcription until some environmental condition, such as the presence of lactose, is met. There are also DNA-binding proteins that stimulate transcription. One particularly well studied example is the catabolite activator protein (CAP), which is also known as the cAMP response protein (CRP). When bound to cAMP, CAP, which also is a sequence-specific DNA-binding protein, stimulates the transcription of lactose- and arabinose-catabolizing genes. Within the lac operon, CAP binds to an inverted repeat that is centered near position -61 relative to the start site for transcription (Figure 31.10). CAP functions as a dimer of identical subunits. 

Some proteins activate transcription by directly contacting RNA polymerase. For example, cyclic AMP, a hunger signal, stimulates the transcription of many catabolic operons by binding to the catabolite activator protein. The binding of the cAMP—CAP complex to a specific site in the promoter region of an inducible catabolic operon enhances the binding of RNA polymerase and the initiation of transcription. 

Catabolic Gene-Activator Protein (CAP) Positively Regulates the lac Operon... 

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