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Collagen may be reprecipitated as obliquely striated fibrils. The oblique striations are due toD-periodic subfibrils staggered axially by approxi­mately 9.0 nm with respect to their neighbours (Bruns, Trelstad & Gross 1973). The diameter of the subfibrils is variable. Optical diffraction analysis of the electron micrographs reveals instances of subfibrils with theD-repeat having diameter 3.7─4.0 nm. We argue that this structure is probably the five-stranded microfibril suggested by Smith (1968).

Although the distribution of hydrophobic residues in the α1 chain collagen sequence has a D ⋍ 670 A periodicity, it is dipoles formed by 100 residues occurring in pairs of unlike charge which are responsible for the 1D stagger between molecules. Sheet models based on the Hodge-Petruska model for the axially projected collagen structure require interactions specifying 1D and 4D staggers. We found no evidence for interactions specifying a strong 4D stagger and, therefore, favour the Smith microfibril model which is specified by 1D stagger interactions alone. Two hydroxylysine residues, 234 residues apart, may form a covalent cross-link stabilising the 1D stagger. Gene duplication does not appear to be responsible for the periodicity in the sequence.

The amino acid sequence in the triplet region of the α1 chain of collagen was analyzed for complementary relationships that would explain the stagger of multiples of 670 A between the rod-like molecules in the fibril. The analysis was done by moving the sequence of 1011 amino acids past itself and scoring for complementarity between opposing amino acids allowing a range of ±2 to 3 residues. It was found that interactions between amino acids of opposite charge and between large hydrophobic amino acids in the overlapping region between two chains are maximal when the chains are staggered by 0D, 1D, 2D, 3D and 4D, where D = 234 ± 1 residues. The residue repeat derived from this value is 2.86 ± 0.02 A. The existence of a D separation between interacting residues was shown to be reflected in the actual distribution of large hydrophobic amino acids. Surprisingly, the distribution approximates the pattern ( 2D 11 )5( D 11 ) repeated over 4.4D intervals. The regularity may arise from structural constraints imposed by super-coiling. The distribution of charged residues is less regular and does not show a well-defined periodicity. However, positively-charged residues tend to be near negatively-charged residues, allowing intramolecular charge neutralization as well as strong intermolecular charge interactions at 0D.

This article reviews some of the literature pertaining to futures markets. After briefly considering how the evolution of the institution of futures trading has required changing interpretations, we devote a longer section to the interplay between theory and evidence concerning intertemporal price relationships. While disputed and inconclusive interpretations persist, Working's theory of the price of storage and his revision of hedging doctrine are clear landmarks of progress in understanding these price relationships. We deal separately with hedging theory; then with the relation between futures and price variability; and finally with the stochastic attributes of futures prices.