In:
European Journal of Biochemistry, Wiley, Vol. 262, No. 2 ( 1999-06), p. 417-425
Abstract:
Kinetic and molecular properties of the Ca 2+ /H + antiporter in the vacuolar membrane of mung bean hypocotyls were examined and compared with Ca 2+ ‐ATPase. Ca 2+ transport activities of both transporters were assayed separately by the filtration method using vacuolar membrane vesicles and 45 Ca 2+ . Ca 2+ uptake in the presence of ATP and bafilomycin A 1 , namely Ca 2+ ‐ATPase, showed a relatively low V max (6 nmol·min −1 ·mg −1 protein) and a low K m for Ca 2+ . The Ca 2+ /H + antiporter activity driven by H + ‐pyrophosphatase showed a high V max (25 nmol·min −1 ·mg −1 ) and a relatively high K m for Ca 2+ . The cDNA for mung bean Ca 2+ /H + antiporter (VCAX1) codes for a 444 amino‐acid polypeptide. Two peptide‐specific antibodies of the antiporter clearly reacted with a 42‐kDa protein from vacuolar membranes and a cell lysate from a Escherichia coli transformant in which VCAX1 was expressed. These observations directly demonstrate that a low‐affinity, high‐capacity Ca 2+ /H + antiporter and a high‐affinity Ca 2+ ‐ATPase coexist in the vacuolar membrane. It is likely that the Ca 2+ /H + antiporter removes excess Ca 2+ in the cytosol to lower the Ca 2+ concentration to micromolar levels after stimuli have increased the cytosolic Ca 2+ level, the Ca 2+ ‐ATPase then acts to lower the cytosolic Ca 2+ level further.
Type of Medium:
Online Resource
ISSN:
0014-2956
,
1432-1033
DOI:
10.1046/j.1432-1327.1999.00377.x
Language:
English
Publisher:
Wiley
Publication Date:
1999
detail.hit.zdb_id:
1398347-7
detail.hit.zdb_id:
1464377-7
SSG:
12
