Exocrine molecules

Amongst the secretions of specialised exocrine complexes, the ancillary products which act as sticky compounds are large, often proteinaceous, molecules. Their primary, secondary and tertiary structures being inherently complex are now seen as ideal informational vehicles — alone or in combination with volatile molecules. Much recent work (Sec. 3.2, below) has identified them as the key components involved in close range transmission, and in intra-nasal peri-receptor events. Proteins are semiochemically implicated when their selective removal or presentation alters responsiveness (Belcher et al., 1990 Mucignat-Caretta et al, 1995). 

Enzyme replacement therapy (ERT) is a therapeutic approach in which the specific enzyme that is absent or inactive in affected individuals is replaced with a functional enzyme molecule. Pancreatic enzyme preparations of porcine or bovine origin have been available in the United States for treatment of exocrine pancreatic insufficiency (EPI) in children and adults with cystic fibrosis and chronic pancreatitis since before the enactment of the Federal Food, Drug and Cosmetic Act of 1938 (ref FDA guidance on EIP April 2004). A... 

The J (joining) chain (reviewed by Koshland, 1975 and 1985 [124,125]) is a polypeptide chain of a molecular weight of about 15000. Unlike heavy and light chains, which contribute to all immunoglobulin molecules, the J chain is only attached covalently via disulphide bridges to the Fc portion of secreted IgM and IgA [126,127]. J chain associated with IgM or IgA shows a high affinity for the secretory component protein [128] and it is therefore believed to be necessary for rapid transport through secretory epithelial cells into exocrine fluids [129],... 

In the exocrine pancreatic cells. In many animal cells, the combined force of the Na" concentration gradient and membrane electric potential drives the uptake of amino acids and other molecules against their concentration gradient by lon-llnked symport and antiport proteins (see Section 7.4). And the conduction of action potentials by nerve cells depends on the opening and closing of Ion channels In response to changes In the membrane potential (see Section 7.7). 

Dietary uptake of purine and pyrimidine bases is minimal. The diet contains nucleic acids and the exocrine pancreas secretes deoxyribonuclease and ribonucle-ase, along with the proteolytic and lipolytic enzymes. This enables digested nucleic acids to be converted to nucleotides. The intestinal epithelial cells contain alkaline phosphatase activity, which will convert nucleotides to nucleosides. Other enzymes within the epithelial cells tend to metabolize the nucleosides to uric acid, or to salvage them for their own needs. Approximately 5% of ingested nucleotides will make it into the circulation, either as the free base or as a nucleoside. Because of the minimal dietary uptake of these important molecules, de novo synthesis of purines and pyrimidines is required. 

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