Collagen gelatin transitions

Collagen. Bensusan and Nielsen (1964) have obtained information on the mechanism of the gelatin - collagen-fold transition by a direct experimental approach of determining the rate of formation of hydrogen bonds between peptide... 

When the collagen rod can be extracted in the native form it is soluble in acidic solutions, at room temperature. If the solutions are heated, the collagen is denaturated the chains lose their helical conformation. The characteristic temperature of this helix —> coil transition is around 36 C. The solution then contains principally single chains, but also some double and triple chains which were initially covalently bound and some sub-units of the single chains. This product is gelatin. 

The collagen gelatin transformation in solution has been recognized as a reversible first-order phase transition, subject to the same physical laws which govern the crystalline amorphous phase transitions observed in systems of linear polymers. The direct relationship between the transition in solution and the well-known thermal shrinkage phenomenon exhibited by collagen fibers has also been established. 

Wc turn now to a more detailed consideration of how the multistranded collagen molecule is held together and stabilized in the native state, by examining the events which take place when this stabilization breaks down during the collagen —+ gelatin transition. 

Dilute Solution Studies of the Collagen —> Gelatin Transition... 

Fig. 17. The collagen — gelatin transition for various collagens, measured vis-cometrically. (From Doty and Nishihara, 1958.)...

The temperature at which a given soluble collagen undergoes the collagen —> gelatin conversion (defined either as Td or T,n) is a useful parameter for identification and characterization purposes. However, the transition temperature is constant only when measured in relatively dilute salt... 

Fig. 18. Comparison between the rate of the collagen — gelatin transition for soluble calfskin collagen at 35.9 C, measured as the fractional change in specific viscosity (solid line) and specific rotation (dotted line). (From Doty and Nishihara, 1958.)...

The interaction between proteases and their inhibitors is, at least by comparison with interactions which take place in food systems, a remarkably simple and straightforward association. Simple correlations of functional properties with different kinds of molecular forces cannot be made. It is possible, however, to illustrate the importance of protein structure and of protein—protein interactions as determinants of the functional properties of food proteins. I would like therefore to look at several food systems in which protein—protein or protein—other constituent interactions play a role and examine the relationship between functionality and protein structure in these systems. One of the simplest areas in which to examine this relationship is the well studied collagen-gelatin transition. 

In addition, the native collagen content can be calculated for soluble type I collagen by determination of the loss of optical rotation during the transition to gelatin. Nagelschmidt and Viell (1987) report that at 365 nm the specific optical rotation of type I collagen is between -1029° and -1334° while after denaturation it is between -382° and -509°. 

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