Ca2+-ATPase activity in pancreatic acinar plasma membranes. Regulation by calmodulin and acidic phospholipids

A high degree of ATP hydrolytic activity present in purified rat pancreatic acinar cells was localized to plasma membranes. This activity was stimulated almost equally by Mg2+ or Ca2+. Kinetic analysis revealed that the enzyme had a higher affinity for Ca2+ (Kd = 1.73 microM) than Mg2+ (Kd = 2.98 mi...

Full description

Saved in:
Bibliographic Details
Published in:The Journal of biological chemistry 1984-11, Vol.259 (21), p.13442-13450
Main Authors: Ansah, T A, Molla, A, Katz, S
Format: Article
Language:English
Subjects:
Adenosine Triphosphatases - metabolism
Analytical, structural and metabolic biochemistry
Animals
Biological and medical sciences
Ca(2+) Mg(2+)-ATPase
Calcium-Transporting ATPases - isolation & purification
Calcium-Transporting ATPases - metabolism
Calmodulin - pharmacology
Cations, Divalent
Cell Membrane - enzymology
Edetic Acid - pharmacology
Enzymes and enzyme inhibitors
Female
Fundamental and applied biological sciences. Psychology
Hydrolases
In Vitro Techniques
Kinetics
Molecular Weight
Pancreas - cytology
Pancreas - enzymology
Phospholipids - pharmacology
Rats
Rats, Inbred Strains
Sodium-Potassium-Exchanging ATPase - metabolism
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:A high degree of ATP hydrolytic activity present in purified rat pancreatic acinar cells was localized to plasma membranes. This activity was stimulated almost equally by Mg2+ or Ca2+. Kinetic analysis revealed that the enzyme had a higher affinity for Ca2+ (Kd = 1.73 microM) than Mg2+ (Kd = 2.98 microM) but a similar maximal rate of activity. A comparison of substrate requirements revealed very similar profiles for the Mg2+- and Ca2+-stimulated activities. Combinations of saturating concentrations of Mg2+ or Ca2+ produced the same degree of maximal activity. Investigation of the partial reactions of the ATPase activity revealed two phosphoprotein intermediates (Mr = 115,000 and 130,000) in the presence of Ca2+ and Mg2+. A significant stimulation of the Ca2+-ATPase activity by calmodulin was observed (Kd = 0.7 microM). Calmodulin increased the Ca2+-sensitivity of this enzyme system; Mg2+ appeared to be required for this effect. The Ca2+-ATPase activity was also stimulated by acidic phospholipids. Using an 125I-labeled calmodulin gel overlay technique, calmodulin was shown to bind in a Ca2+-dependent fashion to 133,000- and 230,000-dalton proteins present in the plasma membrane-enriched fraction. Under conditions that favor Ca2+-dependent kinase activity, calmodulin enhanced the phosphorylation of a 30,000- and 19,000-dalton protein. The major ATP hydrolytic activity in pancreatic acinar plasma membranes was present as an ectoenzyme.
ISSN:0021-9258
1083-351X
DOI:10.1016/S0021-9258(18)90714-3