Effect of calcium on rat intestinal alkaline phosphatase activity and molecular aggregation.
Two fractions of rat intestinal alkaline phosphatase (IAP) were detected by Western blot: 168 +/- 6 and 475 +/- 45 kDa. The low molecular weight fraction constitutes 43% of the isolated proteins exhibiting 82% of the enzymatic activity, and a heavier fraction constitutes 57% of the isolated proteins and has 18% of the enzymatic activity. Calcium produced an increase of the 475-kDa form to the detriment of the 168-kDa form. This work also describes the kinetic and structural changes of IAP as a function of calcium concentration. With [Ca2+] < 10 mmole/L, the Ca(2+)-IAP interaction fitted a binding model with 7.8 +/- 4.4 moles of Ca2+ /mole of protein, affinity constant = 19.1 +/- 8.4 L/mmole, and enzymatic activity increased as a linear function of [Ca2+] (r = 0.946 p < 0.01). On the other hand, with [Ca2+] > 10 mmole/L the data did not fit this model and, the enzymatic activity decreased as a function of [Ca2+] (r = - 0.703 p < 0.05).
Brun
Lucas R M
LR
Laboratorio Biologia Osea, Facultad de Ciencias Médicas, Universidad Nacional de Rosario, Rosario, Argentina.
Brance
María L
ML
Rigalli
Alfredo
A
Puche
Rodolfo C
RC
D000469:Alkaline Phosphatase / Q000302:isolation & purification / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002850:Chromatography, Gel; D004305:Dose-Response Relationship, Drug; D005260:Female; D007422:Intestines / Q000201:enzymology*; D007700:Kinetics; D051381:Rats; D011919:Rats, Inbred Strains
D000469:Alkaline Phosphatase; D002118:Calcium