Collagen processing

Despite these observations, there are some common processing techniques that are emerging in the area of processing of biologies, as self-contained biomedical devices become more widely utilized. We examine two such areas in this section collagen processing and surface modification. 

After the secretion into the extracellular space, collagen molecules may be modified chemically even more. Some collagen processing enzymes cleave the procollagen molecules to mature tissue type molecules. Lysine and 5-hydroxylysine residues can be modified enzymatically to allysine (alpha-aminoadipic-acid delta-semialdehyde) and hydroxyallysine (delta-hydroxy, alpha-aminoadipic acid delta-semialdehyde), respectively, by lysyl oxidase (protein-lysine 6-oxidase) (EC 1.4.3.13). The aldehyde group then interacts with the amino group of an adjacent lysine residue to form a Schiff base. Many... 

Other mutations of fibrillar collagen, or mutations that affect collagen-processing, cause Ehlers-Danlos syndrome (EDS), a group of heritable connective tissue disorders causing skin hyperextensibility, articular hypermobility, and tissue fragility. The 3 major types are classic (EDS-I and EDS-II), hypermobility (EDS-III) and vascular (EDS-IV). 

The metzincin catalytic domain consists of a flat surface within a small cleft within which peptide substrates bind and are hydrolyzed (Fig. 8.2a). In astacins, the catalytic domain is stable, but adamalysins require a calcium ion to stabilize the flat surface of the domain above the cleft. Matrilysins require two calcium ions and a second, noncatalytic zinc ion to stabilize this domain (Fig. 8.3). Table 8.3 reviews the roles of specific metal ions that participate in the various stages of collagen processing discussed in this chapter and Chap. 7. 

Table 8.3 Metal ions required for collagen processing...

Kelman, C.D. and DeVore, D.P. (1994) Human collagen processing and auto implant use. U.S. Patent ... 

Bone Formation The building of new bone through osteoblasts. Bone formation, which is part of the bone remodelling process, includes the synthesis of organic matter (mostly collagen type 1) and subsequent mineralisation. 

In the interstitium, angiotensin II induces proliferation of mesangial cells and fibroblasts and the synthesis of collagen and other matrix molecules by these cells via the ATI receptor. Moreover, by the concomitant stimulation of chemoattractant cytokines, inflammation is induced. These processes are mediated by endothelin, transforming growth factor(3, and reactive oxygen species, and finally lead to interstitial fibrosis and glomerulosclerosis observed in hypertension and diabetes. 

The properties described above have important consequences for the way in which these skeletal tissues are subsequently preserved, and hence their usefulness or otherwise as recorders of dietary signals. Several points from the discussion above are relevant here. It is useful to ask what are the most important mechanisms or routes for change in buried bones and teeth One could divide these processes into those with simple addition of new non-apatitic material (various minerals such as pyrites, silicates and simple carbonates) in pores and spaces (Hassan and Ortner 1977), and those related to change within the apatite crystals, usually in the form of recrystallization and crystal growth. The first kind of process has severe implications for alteration of bone and dentine, partly because they are porous materials with high surface area initially and because the approximately 20-30% by volume occupied by collagen is subsequently lost by hydrolysis and/or consumption by bacteria and the void filled by new minerals. Enamel is much denser and contains no pores or Haversian canals and there is very, little organic material to lose and replace with extraneous material. Cracks are the only interstices available for deposition of material. 

Part of the diet consists of fats, which are triglycerol esters of fatty acids (FAs). The FAs from digestion of ingested fats can be metabolized in a variety of pathways. Fragments of the original FAs are preserved in these processes and can be utilized in the biosynthesis of other molecules. It is important to note that, during metabolism, almost all FAs are broken down into two-carbon units. The only exceptions are FAs with odd numbers of carbon atoms these are relatively rare in the diet. It ean be shown further that there is a partial barrier to the incorporation of FA-derived carbon into the amino acids which constitute collagen. 

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