摘要：

A number of physical methods have been used to show that soluble collagen prepared by citrate extraction of carp swim bladder tunics (ichthyocol) consists of rigid, rod-shaped molecules having a very narrow size distribution. The diameter is 13.6 A., and the weight average molecular length and weight are 3000 . and 345,000, respectively. This very asymmetric molecule undergoes denaturation in dilute salt solution at about 30° with an activation energy of 81 kcal, to form a product known as parent gelatin. However, the tendency toward reaggregation below this temperature and the significant rate of hydrolysis above this temperature (energy of activation 24 kcal.) creates unusual difficulty in characterizing the denatured state. The demonstration that 2 M KCNS lowers the denaturation temperature below 4° makes possible the avoidance of reaggregation by the use of this solvent. The number and weight average molecular weights were then shown to be 125,000 ± 10,000 and 138,000 ± 8000, respectively. The ratio of the molecular weight of collagen to the denatured form (parent gelatin) was found to be 2.5 ± 0.15 in separate experiments involving heating directly in the light scattering cell. The interpretation of these data shows that three molecules are formed from each collagen molecule upon denaturation, but the ratio of 2.5 requires that the molecules be of substantially different molecular weights. The dimensions of the collagen molecule are so much larger than the main long spaced periodicity (700 .) in collagen fibrils that several, probably four, of these must be contained within each molecule. Moreover, the size of the average parent gelatin molecule is such that it can traverse the whole length of the collagen molecule. A comparison with the three-stranded collagen structures recently deduced from X-ray studies shows that the observed mass-to-length ratio of 110 is sufficiently close to the required value and that the observed diameter is in excellent agreement. The conclusion therefore follows that the soluble collagen molecule is composed of three polypeptide strands running lengthwise and that it does serve without serious modification as the structural element of collagen fibrils. Moreover, this molecule has the additional characteristics of a hypothetical particle, tropocollagen, which Schmitt, Gross and Highberger concluded must exist as the common building unit of the three forms of collagen observed electron microscopically. Finally, suggestions are made of ways in which the three chains may be mutually arranged in the molecule so as to provide for a dangling chain at one end and a double chain at the other. These rather unique arrangements permit a closer fit of our data and a basis of constructing polarized protofibrils without the need of a continuous primary bonded framework.

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