FUNCTIONAL IMPLICATIONS RESULTING FROM DISRUPTION OF THE CALCIUM-BINDING LOOP IN BOVINE ALPHA-LACTALBUMIN

被引:13
作者
BERLINER, LJ
MEINHOLTZ, DC
HIRAI, Y
MUSCI, G
THOMPSON, MP
机构
[1] NIPPON MED COLL,DEPT BIOCHEM,TOKYO 113,JAPAN
[2] UNIV ROME LA SAPIENZA,DEPT BIOCHEM SCI,I-00185 ROME,ITALY
[3] USDA ARS,EASTERN REG RES CTR,PHILADELPHIA,PA 19118
关键词
CALCIUM-BINDING LOOP DISRUPTION; FUNCTIONALITY; ALPHA-LACTALBUMIN;
D O I
10.3168/jds.S0022-0302(91)78413-0
中图分类号
S8 [畜牧、 动物医学、狩猎、蚕、蜂];
学科分类号
0905 ;
摘要
The strong calcium-binding site of alpha-lactalbumin comprises the carboxylate side chains of aspartic acid 82, 87, and 88 and the carbonyl oxygens of residues 79 and 84. A single methionine residue was selectively modified by controlled CNBr cleavage to yield homoserine at position 90. The CNBr-cleaved alpha-lactalbumin lost the ability to bind calcium strongly as monitored by intrinsic fluorescence, electrophoretic mobility, atomic absorption, and x-ray fluorescence. Remarkably, the modified protein was still competent in lactose biosynthesis, although activity was reduced to 1/40th that of the native form of the protein. Although the strong calcium-binding site was destroyed as a result of the cleavage of the calcium-binding loop, a secondary calcium site was retained that directly affects a rate enhancement of lactose biosynthesis when saturated, resulting in approximately a two- to threefold increase in rate at 1mM CaCl2 with an activation equilibrium constant of 350 +/- 40-mu-M.
引用
收藏
页码:2394 / 2402
页数:9
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