Thermal and surface behavior of yeast protein fractions from Saccharomyces cerevisiae

An easy and inexpensive method of fractionation of a yeast homogenate was proposed and it is based on differential centrifugation steps of insoluble components and subsequent precipitations of soluble fractions. In this fractionation, the effect of addition of protease inhibitor was studied. The procedure, which was performed in mild conditions in order to minimize protein denaturation, produced four fractions that proceed from distinct parts of the yeast cell and with a different chemical composition: Fr I, Fr II, Fr III and Fr IV. Thermal and surface behavior of these samples was also analyzed. Fr I and Fr II, mainly composed by cell wall debris and membrane cell components, respectively, exhibited an adsorption rate (Δγ/Δt1/2) ten-fold higher than Fr III and Fr IV, composed by nucleoproteins and cytoplasmic proteins. All fractions exhibited a unique DSC endotherm with different peak temperature (Tp) and enthalpy values (ΔH). Fr IV exhibited the highest Tp value (74 °C) and less affected by inhibitor absence. Fr I and Fr II showed the highest ΔH values (27–47 J/g protein) but they were markedly affected reducing their enthalpy values and increasing their surface properties in absence of protease inhibitor.