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Active calcium transport via coupling between the enzymatic and the ionophoric sites of Ca2+ + Mg2+-ATPase

✍ Scribed by Shamoo, Adil E. ;Scott, Terrence L. ;Ryan, Thomas E.

Publisher
Wiley (John Wiley & Sons)
Year
1977
Tongue
English
Weight
566 KB
Volume
6
Category
Article
ISSN
0091-7419

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✦ Synopsis

Abstract

The 20K dalton fragment of Ca^2+^ + Mg^2+^‐ATPase obtained from the tryptically digested sarcoplasmic reticulum has been further purified using Bio‐Gel P‐100. This removed low‐molecular‐weight UV‐absorbing and positive Lowry‐reacting contaminants. The ionophoric activity of the 20K fragment in both oxidized cholesterol and phosphatidylcholine: cholesterol membranes is unaltered by this further purification. The 20K selectivity sequence in phosphatidylcholine: cholesterol membranes is Ba^2+^ > Ca^2+^ > Sr^2+^ > Mn^2+^ Mg^2+^.

Digestion of intact sarcoplasmic reticulum vesicles with trypsin, which results in the dissection of the hydrolytic site (30K) from the ionophoric site (20K), is shown to disrupt energy transduction between ATP hydrolysis and calcium transport. This further implicates the 20K dalton fragment as a calcium transport site.

These data and previous evidence are discussed in terms of a proposed model for the ATPase molecular structure and the mechanism of cation transport in sarcoplasmic reticulum.

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