Isolation and characterization of isoforms of retinol binding protein by isoelectrofocusing.
Retinol binding protein prepared from human urine was fractionated by chromatofocusing into four isoforms: two retinol-containing (holo-) and two retinol-free (apo-) species. The pl values of the isoforms ascertained by isoelectrofocusing with an immobiline pH gradient were: holo(I) 4.79-4.77; apo(II) 4.61-4.56; holo(III) 4.63 and apo(IV) 4.46-4.41. In vitro aging experiments with apo(II) under conditions favoring deamidation (37 degrees C, pH 7-10, 3-28 days) resulted in formation of the more acidic apo(IV)-isoform. The aging rate was consistent with pH increase. It appears that the urinary RBP mixture is composed of two apo-holo pairs: a native form with genuine protein structure and an acidic form generated upon aging.
Minic
Z
Z
Institute of General and Physical Chemistry, University of Belgrade, Yugoslavia. minic@isv.cnrs.gif.fr
Hranisavljevic
J
J
Vucelic
D
D
D004591:Electrophoresis, Polyacrylamide Gel / Q000379:methods; D006801:Humans; D007525:Isoelectric Focusing; D007536:Isomerism; D012177:Retinol-Binding Proteins / Q000032:analysis / Q000302:isolation & purification* / Q000652:urine; D012967:Sodium Dodecyl Sulfate
D012177:Retinol-Binding Proteins; D012967:Sodium Dodecyl Sulfate