Collagen Structures Considered as States of Aggregation of a Kinetic Unit. the Tropocollagen Particle
Year: 1954
Type: article
Abstract: Collagen reconstituted from acid solutions may assume not only the fibrous cross- striated form, having an axial repeating period averaging about 640 A, but also the fibrous long-spacing (FLS) form, having an axial repeating period ranging be- tween 1,500 and 3,000 A and averaging about 2,000 A.1' 2 This suggested the exist- ence of extremely thin collagenous particles having lengths equal to those of the long spacings; it was supposed that the FLS might be formed by end-to-end and lateral aggregation of these particles.When this concept was formulated, we adopted the term "tropocollagen"3 to denote the thin, long particles.It was then discovered4 that a segmental form of collagen long spacing (SLS) may be produced from mildly alkaline salt extracts of collagen by dialysis against citrate buffer or by addition of adenosine triphosphoric acid (ATP) to an acid solution of collagen.This was presumptive morphological evidence in support of the tropocollagen hy- pothesis.The segments have the lengths ascribed to the thin particles, and it was postulated that in this case the tropocollagen particles line up laterally but not linearly.The fact that collagen, FLS, and SLS may be converted into each other is further support of the view that the three forms represent different states of aggregation of a unit particle (tropocollagen).It was also considered possible that, in the biogenesis of collagen, tropocollagen may be the form synthesized by the cells and passed by them into.theground substance, where it is converted into the characteristic fibrous form.Evidence for the existence of tropocollagen is primarily morphological (electron microscopic) and is derived from studies of the structures precipitated from collagen solutions.We have also applied physical-chemical methods designed to give infor- mation concerning the size and shape of the hypothesized particles in solution.These studies have contributed relatively little interpretable data thus far, probably because the particles exist in solution as thin, extremely long aggregates.If the solution contained a large proportion of very long fibrous polymers of tropocollagen, it would be extremely difficult to demonstrate the presence of a small amount of the monomer.In the present paper is summarized the evidence thus far obtained that the vari- ous morphologically distinguishable forms of collagen are mutually interconvertible and that the unit of collagen structure involved in these changes of aggregation is the tropocollagen particle.
Language: English
Subfield: Biomaterials
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2061166048