Suggested to be included in AscH- (ascorbate) recovery and assisting iron absorptions are
proteins known as CYBASC proteins. They can reduce AscH- and contain diheme b. They are
essential membrane cytochrome b561 proteins. From the plant Arabidopsis thaliana, two different
paralogs of CYBASC, Atcytb561-A (A-paralog) and Atcytb561-B (B-paralog) were discovered.
They vary in AscH- and ferric iron chelate reactions and visible-spectral traits. The systemic
organization of a CYBASC member was supplied beforehand by discovering the crystal lattice of
the B-paralog. There are hints that at points 77 (B-K77) and 81 (B-K81) linking the AscH- layer
and the well retained lysine remnants are bonded via hydrogen bonds. The well retained tyrosine
at position 70 (B-Y70) lacks an apparent purpose but its localization reflects the potential
participation in proton-coupled electron transfer. Here we show that B-Y70 performs a crucial role
in the variation of the oxidation-reduction median potential of the high-potential heme, EM (bH)
and in AscH- oxidation too. Our results reinforce the participation of the functionally retained BK77 in balancing the Asc2- dianion. These discoveries are reinforced by the crystal lattice of the
B-paralog, but by comparing biochemical and biophysical traits of both paralogs, hints at marked
and more intricate functions of the analogous remnants A-Y69 and A-K76 in the A-paralog. Our
results highlight the requirement for a high-resolution crystal lattice of the A-paralog to reveal the
variations in functional organization between the two paralogs.