Peptidase, catabolic

Furthermore, there does not appear to be any significant reuptake pump for neuropeptides, so once they are released, they are not recaptured for subsequent reuse (Fig. 1—9). The action of peptides is terminated by catabolic peptidases, which cut the peptide neurotransmitter into inactive metabolites. 

FIGURE 1—9- Neurotransmitter synthesis in a neuropeptidergic neuron. Neurotransmitter synthesis occurs only in the cell body because the complex machinery for neuropeptide synthesis is not transported into the axon terminal. Synthesis of a specific neuropeptide begins with the transcription of the pre-propeptide gene in the cell nucleus into primary RNA, which can be rearranged or edited to create different versions of RNA, known as alternative splice variants or pre-propeptide RNA. Next, RNA is translated into a pre-propeptide, which enters the endoplasmic reticulum, where its peptide tail is clipped off by an enzyme called a signal peptidase to form the propeptide, the direct precursor of the neuropeptide neurotransmitter. Finally, the propeptide enters synaptic vesicles, where it is converted into the neuropeptide itself. Synaptic vesicles loaded with neuropeptide neurotransmitters are transported down to the axon terminals, where there is no reuptake pump for neuropeptides. The action of peptides is terminated by catabolic peptidases, which cut the peptide neurotransmitter into inactive metabolites. 

The NEP and APN levels are moderate on heart [74,75] while the concentration of both peptidases is higher in vascular endothelium or vagus nerve terminals [76-78]. However, the mechanisms and site of action (central or peripheral) involved in the cardioprotective effects of the endogenous opioid peptides remain unknown. Nevertheless, owing to their lack of narcotic effects, inhibition of endogenous enkephalin catabolism and subsequent stimulation of delta receptor could have interesting clinical applications in the cardiovascular domain. 

Biocytin is hydrolyzed by biotinidase, which acts on free or peptide-incorporated biocytin to release biotin, but has no general peptidase or esterase activity. Biotinidase is most active toward free biocytin, but it will also release biotin from biocytin-containing peptides. The activity decreases as the size of the peptide increases, so it is likely that in vivo the catabolism of biotin-containing enzymes is by proteolysis, followed by biotinidase action, rather than the release of biotin, leaving the apoenzyme as a substrate for proteolysis. Biotinidase is found in all tissues, including the pancreatic juice and intestinal mucosa. 

Christensen, J. E., Dudley, E. G., Pederson, J., Steele, J. L. (1999). Peptidases and amino acid catabolism in lactic acid bacteria. Antonie Van Leeuwenhoek, 76, 217-246. 

Fig. 22.2. Lysosomal catabolism of membrane-associated/ hydrophobic proteins. In infantile neuronal ceroid lipofuscinosis (CLNl) palmitoyl protein thioesterase is deficient (22.4.1). Late infantile neuronal lipofuscinosis (CLN2) is due to a defect in tripeptidyl peptidase I (22.4.2). Sub C = subunit C of ATP synthase complex. CLN3 protein = membrane protein of unknown function. It probably contributes to the disposal of organella membranes, it is defective in juvenile neuronal ceroid lipofuscinosis (CLN3, 22.4.3)...

Catabolize the glutathione-herbicide conjugate once inside the vacuole e,g, carboxypeptidases, other peptidases). 

Figure 1.3. Diagram of the proteolytic systems of lactic acid bacteria, (a) Extracellular components PrtP, cell-envelope proteinase PrtM, proteinase maduration protein Opp, oligopetide permease DtpT, the ion linked trasnsporter for di-and tripeptides and Opt, the ABC transporter for peptides, (b) Intracelullar components pool of about 20-25 peptidases, including general (PepN, PepC) and specific (PepX, PepQ) peptidases, and amino acid catabolic enzymes (carboxylases, aminotransferases, etc.).

LAB are able to produce many important aroma cort iounds from amino acid (AA) catabolism (Table 19.1). LAB possess a powerful proteolytic system, in relation to their multiple auxotrophy for AA, which has been reviewed in detail (Fox and Wallace 1997 Christensen et al. 1999 Smit et al. 2005 Steele et al. 2013). LAB hydrolyze proteins into peptides and amino acids, which impact the taste of foods. Large hydrophobic peptides are associated with (undesirable) bitter taste, while peptides and A A contribute to the basic taste of cheese. The hydrolysis of large hydrophobic peptides can be accelerated by the release of intracellular peptidases from lysed LAB cells in cheese paste, in which they remain active during the ripening period, thus decreasing cheese bitterness (McSweeney and Sousa 2000). 

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