Collagen mechanisms

Fibroblasts have another and apparently contradictory capability—namely, the secretion of collagenase, the enzyme that initiates the dissolution of collagen. Mechanisms controlling the creation, extrusion, and deposition of fibrous extracellular components, and the synthesis of dissolution enzymes, are incompletely known. Each of these areas continues to be investigated (Furthmayr, 1982). 

Weadock, K. S., Wolff, D. and Silver, F.H. (1987) Diffusivity of 1-labelled macromolecules through collagen mechanism of diffusion and effect of adsorption. Biomaterials, 8, 105-112. 

Components/ mechanism of action Human plasma, fibrinogen and thrombin, virally inactivated, hemostat, sealant. Autologous fibrinogen -t-platelet-rich plasma, hemostatic gel. Bovine collagen, bovine thrombin, plus autologous human plasma, hemostatic agent. Bovine collagen and bovine thrombin. Expands 20% which aids in hemostatic effect. 

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. 

These mechanisms for the synthesis of glycine present a partial barrier to the movement of FA carbons into this molecule, the most abimdant AA in collagen. On the other hand, proline is synthesized from a-keto glutarate which can be freely derived from either carbohydrates or FAs thus the synthesis of pro line does not present a barrier to entry ofFA-derived carbons into collagen. 

The effect of various chemical modifications on the mechanical properties of reconstituted collagen and the diffusion rates of the steroid medroxyprogesterone was investigated (38). Formaldehyde-treated films, which are heavily crosslinked, have high moduli and low rates of drug release. Films treated with chrome quickly become hydrated in solution and have low moduli and very rapid drug release characteristics. 

Self-assembling systems made of proteins provide many biological systems with essential structural elements, including viral envelopes, bacterial S-layers, microtubules, collagens, and keratins (see Ref. 6 for a review). Detailed studies on in vitro self-assembly optimization were carried out for several systems as a part of an ongoing effort to elucidate the in vivo mechanism. Data reported from such studies may provide an optional basis for the design and in vitro fabrication of nanostructures made of natural proteins (Fig. 1). 

A number of iron-containing, ascorbate-requiring hydroxylases share a common reaction mechanism in which hydroxylation of the substrate is linked to decarboxylation of a-ketoglutarate (Figure 28-11). Many of these enzymes are involved in the modification of precursor proteins. Proline and lysine hydroxylases are required for the postsynthetic modification of procollagen to collagen, and prohne hydroxylase is also required in formation of osteocalcin and the Clq component of complement. Aspartate P-hydroxylase is required for the postsynthetic modification of the precursor of protein C, the vitamin K-dependent protease which hydrolyzes activated factor V in the blood clotting cascade. TrimethyUysine and y-butyrobetaine hydroxylases are required for the synthesis of carnitine. 

Mechanism of NPYR Formation The consistent occurrence of NPYR in fried bacon and cooked-out fat has led to an intensive search for both the precursors and mechanism that could account for its formation. Although model system studies have implicated a number of compounds including proline, collagen, putreseine, spermidine, pyrrolidine and glycyl-L-glycine as possible... 

Meyer, M., Muhlbach, R., and Harzer, D. (2005). Solubilisation of cattle hide collagen by thermo-mechanical treatment. Polym. Degrad. Stab. 87,137-142. 

---