Characteristics of anion-stimulated Mg-ATPase from rat parotid gland secretory granules.
Magnesium-dependent adenosine triphosphatase (Mg-ATPase) was assayed in highly purified secretory granules. The enzyme was stimulated by sulphite and isethionate, unaffected by chloride and inhibited by fluoride and thiocyanate. Inhibition was not related to the permeant properties of the anion, but the relative inhibitory potency of the anions was similar to that in some other studies of secretory granule ATPases. Maximum contribution to the anion-stimulated ATPase by contaminating mitochondria was estimated at 9.3%. The enzyme was inhibited by the stilbene disulphonic acid inhibitor, 4-acetamido-4'-isothiocyano-2,2'-stilbene disulphonic acid (SITS). The IC50 was 0.16 mM in the absence of sulphite and increased in the presence of sulphite. The relation of the inhibition by SITS to sulphite was complex. Both Vmax and Km parameters were changed by SITS. Furthermore the data are consistent with the presence of two anion-stimulated ATPases. The ATPase was sensitive to tributyltin, dicyclohexylcarbodiimide (DCCD) and oligomycin, only moderately sensitive to azide, probenecid and N-ethylmaleimide (NEM) and rather insensitive to carbonylcyanide m-chlorophenylhydrazone (CCCP) and sulphisoxazole. ATPase activity was stimulated by calcium both in the presence and absence of magnesium. These findings suggest that the ATPase(s) present in parotid secretory granules is unique among secretory granule ATPases.
Dowd
F J
FJ
Department of Pharmacology, Creighton University, Omaha, NE 68178.
Pasieniuk
J A
JA
Hand
A R
AR
Cheung
P H
PH
Haines
D W
DW
D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000032:analysis*; D003594:Cytoplasmic Granules / Q000201:enzymology* / Q000648:ultrastructure; D066298:In Vitro Techniques; D008297:Male; D008854:Microscopy, Electron; D010306:Parotid Gland / Q000201:enzymology* / Q000648:ultrastructure; D051381:Rats; D011919:Rats, Inbred Strains
D017301:Ca(2+) Mg(2+)-ATPase