Phosphorylation of the calcium-transporting adenosinetriphosphatase by lanthanum ATP: Rapid phosphoryl transfer following a rate-limiting conformational change

Journal Article · Tue May 29 00:00:00 EDT 1990 · Biochemistry; (United States)

DOI:https://doi.org/10.1021/bi00473a030· OSTI ID:5272196

Hanel, A M; Jencks, W P ^[1]

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1. Brandeis Univ., Waltham, MA (USA)

The calcium-transport ATPase (CaATPase) of rabbit sarcoplasmic reticulum preincubated with 0.02 mM Ca{sup 2+} ({sup c}E{center dot}Ca{sub 2}) is phosphorylated upon the addition of LaCl{sub 3} and ({gamma}-{sup 32}P)ATP with an observed rate constant of 6.5 s{sup {minus}1}. La{center dot}ATP binds to {sup c}E{center dot}Ca{sub 2} while ATP, Ca{sup 2+}, and La{sup 3+} dissociate from {sup c}E{center dot}Ca{sub 2}{center dot}La{center dot}ATP at {le}1 s{sup {minus}1}. The reaction of ADP with phosphoenzyme (EP) formed from La{center dot}ATP is biphasic. An initial rapid loss of EP is followed by a slower first-order disappearance, which proceeds to an equilibrium mixture of EP{center dot}ADP and nonphosphorylated enzyme with bound ATP. The fraction of EP that reacts in the burst ({alpha}) and the first-order rate constant for the slow phase (k{sub b}) increase proportionally with increasing concentrations of ADP to give maximum values of 0.35 and 65 s{sup {minus}1}, respectively, at saturating ADP. The burst represents rapid phosphoryl transfer and demonstrates that ATP synthesis and hydrolysis on the enzyme are fast. The phosphorylation of {sup c}E{center dot}Ca{sub 2} by La{center dot}ATP at 6.5 s{sup {minus}1} and the kinetics for the reaction of EP and ADP are consistent with a rate-limiting conformational change in both directions. The conformational change converts {sup c}E{center dot}Ca{sub 2}{center dot}La{center dot}ATP to the form of the enzyme that is activated for phosphoryl transfer. It is concluded that the reaction mechanism of the CaATPase is remarkably similar with Mg{center dot}ATP and La{center dot}ATP; however, the strong binding of La{center dot}ATP slows both the conformational change that is rate limiting for EP formation and the dissociation of La{center dot}ATP.

• OSTI ID: 5272196
• Journal Information: Biochemistry; (United States), Journal Name: Biochemistry; (United States) Vol. 29:21; ISSN 0006-2960; ISSN BICHA
• Country of Publication: United States
• Language: English

Related Subjects

550201* -- Biochemistry-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
ACID ANHYDRASES
ALKALINE EARTH METAL COMPOUNDS
ANIMALS
ATP
ATP-ASE
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BIOCHEMICAL REACTION KINETICS
CALCIUM COMPOUNDS
CELL CONSTITUENTS
CHEMICAL REACTIONS
CHLORIDES
CHLORINE COMPOUNDS
CONFORMATIONAL CHANGES
DAYS LIVING RADIOISOTOPES
ENDOPLASMIC RETICULUM
ENZYMES
HALIDES
HALOGEN COMPOUNDS
HYDROLASES
ISOTOPES
KINETICS
LANTHANUM CHLORIDES
LANTHANUM COMPOUNDS
LIGHT NUCLEI
MAMMALS
NUCLEI
NUCLEOTIDES
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
PHOSPHOHYDROLASES
PHOSPHORUS 32
PHOSPHORUS ISOTOPES
PHOSPHORYLATION
RABBITS
RADIOISOTOPES
RARE EARTH COMPOUNDS
REACTION KINETICS
SARCOPLASMIC RETICULUM
VERTEBRATES