PMID- 1535623
OWN - NLM
STAT- MEDLINE
DCOM- 19920806
LR  - 20210210
IS  - 0021-9258 (Print)
IS  - 0021-9258 (Linking)
VI  - 267
IP  - 18
DP  - 1992 Jun 25
TI  - Characterization of the inhibition of intracellular Ca2+ transport ATPases by 
      thapsigargin.
PG  - 12606-13
AB  - The effects of thapsigargin (TG), a specific inhibitor of intracellular 
      Ca(2+)-ATPases, were studied on vesicular fragments of sarcoplasmic reticulum 
      (SR) membranes. Inhibition of Ca2+ transport and ATPase activity was observed 
      following stoichiometric titration of the membrane bound enzyme with TG. When 
      Ca2+ binding to the enzyme was measured in the absence of ATP, or when one cycle 
      of Ca(2+)-dependent enzyme phosphorylation by ATP was measured under conditions 
      preventing turnover, protection against TG by Ca2+ was observed. The protection 
      by Ca2+ disappeared if the phosphoenzyme was allowed to undergo turnover, 
      indicating that a state reactive to TG is produced during enzyme turnover, 
      whereby a dead end complex with TG is formed. Enzyme phosphorylation with Pi, ATP 
      synthesis, and Ca2+ efflux by the ATPase in its reverse cycling were also 
      inhibited by TG. However, under selected conditions (millimolar Ca2+ in the lumen 
      of the vesicles, and 20% dimethyl sulfoxide in the medium) TG permitted very low 
      rates of enzyme phosphorylation with Pi and ATP synthesis in the presence of ADP. 
      It is concluded that the mechanism of ATPase inhibition by TG involves mutual 
      exclusion of TG and high affinity binding of external Ca2+, as well as strong 
      (but not total) inhibition of other partial reactions of the ATPase cycle. TG 
      reacts selectively with the state acquired by the ATPase in the absence of Ca2+. 
      This state is obtained either by enzyme exposure to EGTA, or by utilization of 
      ATP and consequent displacement of bound Ca2+ during catalytic turnover.
FAU - Sagara, Y
AU  - Sagara Y
AD  - Department of Biological Chemistry, University of Maryland School of Medicine, 
      Baltimore 21201.
FAU - Fernandez-Belda, F
AU  - Fernandez-Belda F
FAU - de Meis, L
AU  - de Meis L
FAU - Inesi, G
AU  - Inesi G
LA  - eng
PT  - Journal Article
PT  - Research Support, Non-U.S. Gov't
PT  - Research Support, U.S. Gov't, P.H.S.
PL  - United States
TA  - J Biol Chem
JT  - The Journal of biological chemistry
JID - 2985121R
RN  - 0 (Terpenes)
RN  - 67526-95-8 (Thapsigargin)
RN  - 8L70Q75FXE (Adenosine Triphosphate)
RN  - EC 7.2.2.10 (Calcium-Transporting ATPases)
RN  - SY7Q814VUP (Calcium)
SB  - IM
MH  - Adenosine Triphosphate/metabolism
MH  - Animals
MH  - Biological Transport
MH  - Calcium/*metabolism
MH  - Calcium-Transporting ATPases/*antagonists & inhibitors/metabolism
MH  - In Vitro Techniques
MH  - Kinetics
MH  - Phosphorylation
MH  - Rabbits
MH  - Terpenes/*pharmacology
MH  - Thapsigargin
EDAT- 1992/06/25 00:00
MHDA- 1992/06/25 00:01
CRDT- 1992/06/25 00:00
PHST- 1992/06/25 00:00 [pubmed]
PHST- 1992/06/25 00:01 [medline]
PHST- 1992/06/25 00:00 [entrez]
AID - S0021-9258(18)42320-4 [pii]
PST - ppublish
SO  - J Biol Chem. 1992 Jun 25;267(18):12606-13.