3,2,1: A,B,C Sub-unit Hypothesis for the α-Chains of Tropocollagen

Abstract

THE clear-cut demonstration by Piez¹ that the 3 α-chains of cod-fish skin tropocollagen are unique, and the likelihood that a similar condition is true for all species of tropocollagen, have led me to consider various simple arrays of sub-units within the chains which could explain their known compositional features. I have arrived at a model in which an α-chain consists of 6 sub-units, each of approximately 17,000 molecular weight, and falling into 3 different compositional types that I call A, B and C, respectively. A tropocollagen unit, then, in this model would consist of a total of 18 sub-units: 6A, 6B, 6C. Of all the possible combinations of 6 sub-units of 3 types in an α-chain, one which fits the known analyses of the amino-acid compositions of the several types of α-chains in the various tropocollagens is the following: α₁ = 3A + 2B + C; α₂ = 3C + 2A + B; α₃ = 3B + 2C + A For purposes of reference we designate this particular model as the 3,2,1 : A,B,C model, indicating that each different α-chain in the tropocollagen unit consists of a different array of the sub-units, but similar in that it has 3 of one kind of sub-unit, 2 of a second, and 1 of the third.