A change observation of oriented diffraction from low-density serum lipoprotein.

The X-ray diffraction patterns have been recorded from concentrated preparations of low-density serum lipoprotein (LDL). In one case a specimen gave rise to oriented diffraction: the 36 A ring, which has previously been attributed to the cholesteryl esters in LDL, shows markedly oriented intensity; and of the other small-angle rings, which do not show oriented peak intensity, one nonetheless shows significant anisometry. The possibility cannot be ruled out that an artifactual structure has been created; however, it is calculated that the structure will, if exposed in an unoriented preparation, give rise to 36 A diffraction not obviously distinguishable from the native pattern. If valid for the native LDL particle, these observation suggest that the cholesteryl esters in the core of the particle may be arranged in simple planar, or else cylindrically concentric, layers and that the overall shape of the particle is not a uniform sphere.