Peptides physiological functions

The VACM-1 receptor is a membrane-associated protein with a single putative transmembrane domain that binds selectively AVP (XD — 2 nM), but cannot discriminate between VXR and V2R analogues. It is expressed in endothelial and medullary collecting duct cells and upon stimulation by AVP. It induces a mobilization of cytosolic-free Ca2+, decreases cAMP production and inhibits cellular growth via MAPK phosphorylation and p53 expression. The mechanism of action and physiological functions of this new receptor are not well understood, but it seems to participate in the regulation of AVP induced signal transduction pathways or of a yet unidentified peptide. 

The reason that the caseins, which constitute nearly 80% of bovine milk, are unfolded in their native states appears to be to facilitate digestion, since the open rheomorphic structures allow rapid and extensive degradation to smaller peptides by proteolytic enzymes. The natively unfolded structures of many cereal proteins may serve an analogous purpose since they provide nutrition for seedlings. The physiological function of the synucleins in the brain is as yet unclear, but tau is known to promote and stabilize the assembly of microtubules. 

The rapid and relatively recent determination of the structures of so many nematode neuropeptides has resulted in a huge disparity between available structural and functional data indeed, currently the physiological function of any of the known nematode neuropeptides remains unknown. Most of the accumulated data on nematode neuropeptide activities have been obtained using muscle strips of A. suum and, as a result, only provide a glimpse of the putative role for many of the peptides involved. 

There have been sustained efforts in recent years to use the carrier systems of the brush-border membrane of intestinal mucosa to increase absorption of orally administered drugs [29] [30]. One system of particular interest is the intestinal peptide carrier (hPEPTl) whose physiological function is the absorption of di- and tripeptides and whose xenobiotic substrates include /3-lactam antibiotics, renin inhibitors, and angiotensin-converting enzyme (ACE) inhibitors [31]. 

Over 300 peptides isolated in our laboratory were studied in one or more tumor or normal cell cultures [39-44]. Part of the results obtained is summarized in Table 2.3. Over 75% of the peptides showed pronounced proliferative or antiproliferative activity in at least one cell type (Fig. 2.3). As a rule, tumor cells are more sensitive to peptide action. Besides the cell type, experimental conditions such as cell density or composition of the culture medium also affected the overall effect. In several cases (13%, Fig. 2.3) even the sign of the effect was peptide concentration dependent. Generally, experiments with cell cultures conform with the view that the main physiological function of cell and tissue peptidomes is control of long term processes and the homeostatic balance (i.e. cell differentiation, proliferation and elimination). The overall effect of peptide pools is achieved by concerted action of total sets of peptides rather than by single components. The molecular mechanisms of peptide action in cells requires concrete study in each individual case and are the subject of current research. 

A physiological function of a given food that maintains our homeostasis and contributes to our health quality is currently known as a tertiary function of food. In Japan, the Ministry of Health, Labor and Welfare accepts the prophylaxis of lifestyle-related diseases by functional foods. Presently, many functional foods are available in the market as food for specific health use (FOSHU) products. To date, more than 940 items to prevent lifestyle-related diseases such as hypertension, diabetes and hyperlipidemia are accepted as a FOSHU product. Amongst the products, antihypertensive foods are unique rather than others, since their candidates (in most cases, peptides) can improve elevated blood pressure (BP) after intact absorption into our body. 

The importance of peptide hormones has long been realized and in recent years there has been a renewed excitement, with new discoveries made almost daily on the role of peptides in the regulation of physiologic function, and the isolation and characterization of new peptide factors carrying out ttiese roles. The fact that the... 

Recently, marine fish-derived bioactive peptides have been shown to possess many physiological functions including antihypertensive, antioxidant, antimicrobial, antiproliferative, antitumor, anticoagulant, and immunomodulatory activities. Among these, antihypertensive peptides act as ACE inhibitors are of particular interest for prevention and treatment of hypertension (Kobayashi et ah, 2008). 

Serine proteases (SP) are a family of enzymes that use a uniquely activated serine residue in the substrate-binding pocket to catalytically hydrolyze peptide bonds [66], SP carry out a diverse array of physiological functions, of which the best known are digestion, blood clotting, fibrinolysis, fertilization, and complement activation during immune responses [67], They have also been shown to be abnormally expressed in many diseases including cancer, arthritis, and emphysema [42, 43, 67-70],... 

The opioids produce their pharmacological effects by interacting with a closely related group of peptide receptors, thereby suggesting that endogenous opioid-like polypeptides exist, which presumably have a physiological function. 

General tendencies in the in-vivo elimination of proteins and peptides may often be predicted from their physiological function. Peptides, for example, frequently have hormone activity and usually have short elimination half-lives. This is desirable for a close regulation of their endogenous levels and thus function. In contrast, transport proteins such as albumin or a-1 acid glycoprotein have elimination half-lives of several days or weeks, which enables and ensures the continuous maintenance of necessary concentrations in the bloodstream. 

Peptides and proteins exhibit distinct species specificity with regard to structure and activity. Peptides and proteins with identical physiological function may have different amino acid sequences in different species, and may have no activity or be even immunogenic if used in a different species. 

In summary, it is difficult to generalize about dopaminergic control of peptidergic function in the neostriatum. This circumstance is a consequence of the ignorance of the physiological functions regulated by the peptides and the limited number of investigations directed towards neostriatal peptides. 

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