No relationship between enzyme activity and structure of nucleotide binding site in sarcoplasmic reticulum Ca(2+)-ATPase from short-term stimulated rat muscle.
OBJECTIVE
We examined whether structural alterations to the adenine nucleotide binding site (ANBS) within sarcoplasmic (endo) reticulum Ca(2+)-ATPase (SERCA) would account for contraction-induced changes in the catalytic activity of the enzyme as assessed in vitro.


METHODS
Repetitive contractions were induced in rat gastrocnemius by electrical nerve stimulation. Measurements of sarcoplasmic reticulum properties were performed on control and stimulated muscles immediately after or at 30 min after the cessation of 5-min stimulation. In order to examine the properties at the ANBS, the binding capacity of SERCA to fluorescence isothiocyanate (FITC), a competitive inhibitor at the ANBS, was analysed in microsomes.


RESULTS
Short-term electrical stimulation evoked a 23.9% and 32.6% decrease (P < 0.05) in SERCA activity and in the FITC binding capacity, respectively, in the superficial region of the muscle. Whereas SERCA activity reverted to normal levels during 30-min recovery, a restoration of the FITC binding capacity did not occur.


CONCLUSIONS
The discordant changes between the enzyme activity and the FITC binding suggest that, at least during recovery after exercise, changes in SERCA activity may not correlate closely with structural alterations to the ANBS within the enzyme.
Mishima
T
T
Department of Pre-School Education, Hachinohe Junior College, Aomori, Japan.
Kuratani
M
M
Kanzaki
K
K
Yamada
T
T
Matsunaga
S
S
Wada
M
M
D000227:Adenine Nucleotides / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D004558:Electric Stimulation; D016650:Fluorescein-5-isothiocyanate / Q000494:pharmacology; D005456:Fluorescent Dyes / Q000494:pharmacology; D006003:Glycogen / Q000737:chemistry; D019344:Lactic Acid / Q000737:chemistry; D008297:Male; D008861:Microsomes / Q000201:enzymology; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000737:chemistry / Q000201:enzymology*; D018384:Oxidative Stress; D005082:Physical Exertion; D051381:Rats; D017208:Rats, Wistar; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000737:chemistry / Q000378:metabolism*; D013329:Structure-Activity Relationship; D013997:Time Factors
D000227:Adenine Nucleotides; D005456:Fluorescent Dyes; D019344:Lactic Acid; D006003:Glycogen; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D016650:Fluorescein-5-isothiocyanate