Binding of Ca and Mg by lipoprotein and nucleoprotein subfractions of rat liver cell microsomes

✍ Scribed by Carvalho, Arselio P. ;Sanui, Hisashi ;Pace, Nello

• Publisher: Wiley (John Wiley & Sons)
• Year: 1965
• Tongue: English
• Weight: 715 KB
• Volume: 66
• Category: Article
• ISSN: 0095-9898
• DOI: 10.1002/jcp.1030660106

✦ Synopsis

Rat liver cell microsomes were subfractionated in DzO-sucrose solutions of various densities into three subfractions with densities > 1.23, 1.18-1.23 and 1.12-1.18. There was an inverse correlation between the nucleic acid and lipid contents of these subfractions; the highest density subfraction had a relatively high nucleic acid (20.9% ) and low lipid (15.1% ) content and the lowest density subfraction had a low nucleic acid (3.4% ) and a high lipid (45.2% ) content. Whole microsomes were determined to be composed of 55.0% protein, 8.6% nucleic acid and 36.4% lipid. This composition of microsomes was calculated to reflect a nucleoprotein and lipoprotein content of 28% and '72%, respectively. Investigation of Ca and Mg bind- ing by the three microsome subfractions and by the whole microsome fraction after equilibration for 12 hours in a medium of pH 6.7 containing 8-9 meq Ca or Mg/liter indicated that all fractions retained considerable amounts of the divalent cations (1.5-2.6 meq/g N). The nucleoprotein fraction was calculated to bind 0.35-0.40 meq Ca or Mg/g dry weight of nucleoprotein and the lipoprotein fraction 0.12 meq Ca or Mg/g dry weight of lipoprotein. Nevertheless, the lipoprotein fraction of microsomes is responsible for 45% of the total binding of Ca or Mg by the whole microsome fraction. These observations support the contention that cellular membrane structures, composed essentially of lipoprotein, can bind considerable quantities of the divalent cations.