Spherosome membranes: half unit-membranes

Abstract

Spherosomes are bounded by unusual single-line "membranes" which measure 2 to 3.5 nanometers in width, contrasted to the well known tripartite unit-membranes which measure 6 to 8.5 nanometers in over-all thickness. Juxtaposed externally (from the side addressing the hyaloplasm), two spherosomal membranes adjoin to form a thicker single line, but apposed internally (the sides that contact stored lipid) two single-line membranes touch to form a tripartite structure resembling a unit-membrane. Morphologically, we interpret the single-line membranes of spherosomes as half unit-membranes whose polar surfaces face the hyaloplasm and whose lipoidal nonpolar surfaces contact internal storage lipid.Corroboration of this interpretation was shown biochemically by demonstrating the presence of membrane structural protein in peanut spherosomes. In addition, an immunological identity between membrane protein isolated from spherosomes of quiescent seeds and membrane protein extracted from the mitochondrial fraction of 10-day germinated seedlings was observed. We conclude that the atypical, single-line membranes bounding spherosomes are in fact biological membranes that correspond to half unit-membranes.