MICROSTRUCTURE OF EGG YOLK

Abstract

ABSTRACTThe particulate matter of fresh, infertile egg yolk was studied using transmission electron microscopy. Granules in electron micrographs appeared to be composed of electron‐dense subunits. Treatment of granules with 0.34M NaCl removed a considerable amount of matrix particles, and, as a result, subunits each consisting of a large globule overlaid with protein strands having attached electron‐dense micro‐particles, were observed. The structure of the granules was disrupted completely by 1.71M NaCl treatment. Upon ultracentrifugation of granules in 1.71M NaCl, five fractions (two floating and three sedimenting) were formed. The uppermost floating fraction, a semisolid pellicle, was made up of small and large globules with diameters ranging between 30–100 nm. The subpellicle floating fraction consisted of only small globules with diameters about 27 nm and numerous myelin figures. The three sedimenting fractions appeared to be made up of protein strands with attached micro‐particles (presumably lipovitellins). The plasma was made up predominantly of small globules (LDL micelles) which had mottled surfaces but some myelin figures were also present. The diameters of the globules ranged between about 13–50 nm and the median diameter was about 23 nm. Small electron‐dense particles, designated as ultraparticles, were noted on the surfaces of LDL micelles of plasma, These ultraparticles were released from the LDL surfaces when plasma was treated with pepsin. ultraparticles were also noted on surfaces of globules in granules.