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Question: Alpha-spectrin and beta-spectrin subunits form parallel or antiparallel heterodimers?

Context: α- and β-spectrin by LC-MS/MS identifies Cys in these antiparallel chains
antiparallel spectrin heterodimers
alpha- and beta-spectrins are stable as monomeric forms but occur physiologically as alpha,beta-heterodimers
human erythroid alpha-spectrin repeats 13 and 14 (HEalpha13,14) and human erythroid beta-spectrin repeats 8 and 9 (HEbeta8,9), are located opposite each other on antiparallel spectrin dimers.
Spectrins comprise α- and β-subunits made up predominantly of a series of homologous repeating units of about 106 amino acids; the α- and β-chains form antiparallel dimers by lateral association
The spectrin heterodimer is formed by the antiparallel lateral association of an alpha and a beta subunit
Two of the less stably folded fragments, human erythroid alpha-spectrin repeats 13 and 14 (HEalpha13,14) and human erythroid beta-spectrin repeats 8 and 9 (HEbeta8,9), are located opposite each other on antiparallel spectrin dimers.
Influence of lateral association on forced unfolding of antiparallel spectrin heterodimers.
The antiparallel side-to-side association of spectrin alpha and beta monomers is a two-step process which occurs in seconds even at 0 degrees C and at low concentrations.
The spectrin heterodimer is formed by the antiparallel lateral association of an alpha and a beta subunit, each of which comprises largely a series of homologous triple-helical motifs.
Human erythrocyte spectrin is an antiparallel heterodimer comprised of a 280 kDa alpha subunit and a 246 kDa beta subunit which further associates into tetramers in the red cell membrane cytoskeleton
The spectrin heterodimer is formed by the antiparallel lateral association of an alpha and a beta subunit, each of which comprises largely a series of homologous triple-helical motifs
The basic unit of spectrin is an antiparallel heterodimer composed of two homologous chains, beta and alpha
antiparallel