Small high density lipoprotein subclasses: some of their physico-chemical properties and stability in solution

Small high density lipoproteins (SHDL) contribute to the protection from atherosclerosis, but detailed information about their properties is not available yet. We isolated four of the smallest HDL subclasses that contain apoA-I alone, the small lipoprotein A-I (SLpAI), by their separation on gradient polyacrylamide gel followed by electroelution. Their physico-chemical properties were calculated from their displacement in non-denaturing gradient polyacrylamide gel under the effect of electrical potential. The properties are: Stokes’ radii 2.96–3.56 nm; molecular masses 42–70 kDa; net negative charge 7.2–13.5; surface charge densities 3139–4069 –esu ∙ cm–2; surface potentials 10.6–15.7 –mV; coefficients of friction 5.74­–6.90 × 10–8 g ∙ s–1; and diffusion coefficients 5.76–6.94 × 10–7 cm2 ∙ s–1. We found that these particles were of low stability as they underwent molecular transformation into larger particles on storage. The estimated dimensions of these particles do not support ellipsoidal shape, therefore, the most probable shape is spherical; consequently, their hydrated characteristics were estimated. We conclude that these particles have high values of negative surface charge and diffusion coefficients, and are of low stability. Their small Stokes’ radii were similar to each other and they are spherical and highly hydrated.