Turnover of Collagen and Tissue Repair

Hydroxyproline is rapidly metabolized in a pathway initiated by the enzyme hydroxyproline oxidase (Chapter 17). 

Hydroxyproline is present in Clq, which is synthesized at a rate estimated to be about 4.5 mg/kg per day. 

The first aspect has been overcome by measurement of urinary hydroxyproline in individuals with an inherited deficiency of hydroxyproline oxidase. Such persons excrete 

3 g of hydroxyproline per day in urine, which corresponds to about 2.25 g of hydroxyproline-containing proteins, most of which is collagen. Total protein catabolism in a normal well-fed adult is about 300 g thus, collagen catabolism constitutes only about 0.8% of total protein catabolism. 

Collagen turnover has important clinical implications. The location, amount, type, and form of collagen depend on the coordinated control of its synthesis and degradation. In tissue injury (physical, chemical, infectious, or radiation), repair process comprises regeneration and fibrous connective tissue formation. Regeneration is the most desirable form of repair a cut surface of an epidermis is replaced with new epidermis scattered dead liver cells are replaced with new liver cells. 

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