In blood plasma of patients we have discovered an enzyme responsible for the decrease of sialic acid in lipoprotein particle. It was called trans-sialidase. This enzyme is protein of sixty-five kilodaltons. It has three ph-optima – three, five and seven. Enzymatic activity is stimulated by calcium and magnesium ions. Trans-sialidase removes sialic acid from lipoprotein particles and some glycoconjugates and transfers it to other substrates.