Tissue hydroxyproline

The experience with hydroxyproline measurement in tissue hydrolysates differs distinctly from that with urine and plasma hydroxyproline determinations. In tissues, methods have not been as carefully evaluated results have been much more variable both within and between the 

The list of tissue hydroxyproline measurements in experimental animals is long in general three types of investigation have been carried out  

Disorders of the skin and of the blood vessels have been studied by the measurement of hydroxyproline in these tissues (Bll, C9, K2, Sll, S25, VI) skin samples have been used as an index of the general state of maturation of collagen in various disorders (H6). Hydroxyproline measurements in cardiac muscle have been used to quantify the degree of fibrosis from various cardiac diseases (C9, M19). Measurements have been made in amniotic fiuid (K12), in the uterus at various stages (H2, W9), and in the whole body of infants (P5). 

The 6-8-fold increase in total collagen in the uterus with pregnancy, as well as the rapid loss of this relatively inert substance postpartum, has made uterine tissue a favorite for the study of rapid connective tissue turnover and the mechanisms involved, particularly the mechanism of rapid catabolism of such large amounts of insoluble collagen (H2, W9). The availability of human uterine tissue has enhanced the interest in these studies however, they are not yet strictly pertinent to the understanding of disease and will not be further considered here (see W9). 

Cardiac muscle hydroxyproline, measured by a simple colorimetric procedure with inadequate specificity in this situation, increased slightly beyond age 35-40, while a similar rise was seen in the hydroxyproline of aortic tissue (C9). Other studies using identical methods showed no change with age in aortic and pulmonary artery hydroxyproline (Bll, K2). The influence of both age and cardiac hypertrophy on cardiac 

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Hurych and Chvapil have implicated free tissue hydroxyproline as a breakdown product of newly formed soluble collagens in labeled studies in animals. These implications have not been studied in man (H13). 

It is clear from these studies that measurements of tissue hydroxyproline in man have not progressed to the stage of hydroxyproline measurements in urine or plasma. With the availability of more specific techniques, it seems likely that the study of tissue hydroxyproline will play an increasing role in our understanding of disorders in which fibrosis and altered connective tissue are prominent. 

FIGURE 4.4 The structures of several atniuo acids that are less cotntnou but nevertheless found in certain proteins. Hydroxylysine and hydroxyproline are found in connective-tissue proteins, pyroglutatnic acid is found in bacteriorhodopsin (a protein in Halohacterium halohium), and atninoadipic acid is found in proteins isolated from corn. 

Sporophytic maize tissues Biochemical and tissue print analyses of hydroxyproline-rich glycoproteins Hood et al. (11)... 

The many (possibly more than 30) types of collagens found in human connective tissues have substantially the same chemical structure consisting mainly of glycine with smaller amounts of proline and some lysine and alanine. In addition, there are two unusual amino acids, hydroxyproline and hydroxylysine, neither of which has a corresponding base-triplet or codon within the genetic code. There is therefore, extensive post-translational modification of the protein by hydroxylation and also by glycosylation reactions. 

Collagen synthesized in the absence of ascorbic acid (i.e. without hydroxyproline) cannot form its usual stable structure. Collagen is a major component of the structural and connective tissues of the body bone, cartilage, tendons, ligaments, teeth, and skin. Small wonder that things sort of fall apart in the absence of adequate ascorbic acid to support the activity of prolyl hydroxylase. 

Jamall IS, Finelli VN and Quee Hee SS (1981) A simple method to determine nanogram levels of 4-hydroxyproline in biological tissues. Anal Biochem 112, 70-75. 

Collagen is the quantitatively most important protein in mammals, making up about 25% of the total protein. There are many different types of collagen, particularly in connective tissue. Collagen has an unusual amino acid composition. Approximately one-third of the amino acids are glycine (Gly), about 10% proline (Pro), and 10% hydroxyproline (Hyp). The... 

Cell metabolism induction. Methanol extract of STE, in collagen-producing cells, stimulated glycolysis by 80% in cartilage but was not affected in the other tissues. Medium alkaline phosphatase activity was unaffected. In the frontal bone and cartilage, [ H]hydroxyproline and [ H]proline contents were decreased. Neither was affected in the aorta. 

In addition to the 20 common amino acids, proteins may contain residues created by modification of common residues already incorporated into a polypeptide (Fig. 3-8a). Among these uncommon amino acids are 4-hydroxyproline, a derivative of proline, and 5-hydroxylysine, derived from lysine. The former is found in plant cell wall proteins, and both are found in collagen, a fibrous protein of connective tissues. 6-N-Methyllysine is a constituent of myosin, a contractile protein of muscle. Another important uncommon amino acid is y-carboxyglutamate, found in the bloodclotting protein prothrombin and in certain other proteins that bind Ca2+ as part of their biological function. More complex is desmosine, a derivative of four Lys residues, which is found in the fibrous protein elastin. 

The principal protein of skin and connective tissue is called collagen and is primarily constituted of glycine, proline, and hydroxyproline. Collagen is made up of tropocollagen, a substance with very long and thin molecules (14 X 2900 A, MW about 300,000). Each tropocollagen molecule consists of three twisted polypeptide strands. When collagen is boiled with water, the... 

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