Data from: ‘Venus trapped, Mars transits’: Cu and Fe redox chemistry, cellular topography and in situ ligand binding in terrestrial isopod hepatopancreas

Woodlice efficiently sequester copper (Cu) in ‘cuprosomes’ within
hepatopancreatic ‘S’ cells. Binuclear ‘B’ cells in the hepatopancreas form
iron (Fe) deposits; these cells apparently undergo an apocrine secretory
diurnal cycle linked to nocturnal feeding. Synchrotron-based m-focus X-ray
spectroscopy undertaken on thin sections was used to characterize the
ligands binding Cu and Fe in S and B cells of Oniscus asellus (Isopoda).
Main findings were: (i) morphometry confirmed a diurnal B-cell apocrine
cycle; (ii) X-ray fluorescence (XRF) mapping indicated that Cu was
co-distributed with sulfur (mainly in S cells), and Fe was co-distributed
with phosphate (mainly in B cells); (iii) XRF mapping revealed an intimate
morphological relationship between the basal regions of adjacent S and B
cells; (iv) molecular modelling and Fourier transform analyses indicated
that Cu in the reduced Cuþ state is mainly coordinated to thiol-rich
ligands (Cu–S bond length 2.3 A˚ ) in both cell types, while Fe in the
oxidized Fe3þ state is predominantly oxygen coordinated (estimated Fe–O
bond length of approx. 2 A˚ ), with an outer shell of Fe scatterers at
approximately 3.05 A˚ ; and (v) no significant differences occur in Cu or
Fe speciation at key nodes in the apocrine cycle. Findings imply that S
and B cells form integrated unit-pairs; a functional role for secretions
from these cellular units in the digestion of recalcitrant dietary
components is hypothesized.