Barrientos L, Scott J J, Murthy P P
Chemistry Department, Michigan Technological University, Houghton 49931.
Plant Physiol. 1994 Dec;106(4):1489-95. doi: 10.1104/pp.106.4.1489.
Phytases are the primary enzymes responsible for the hydrolysis of phytic acid, myo-inositol-1,2,3,4,5,6-hexakisphosphate (I-1,2,3,4,5,6-P6). A number of phytases with varying specificities, properties, and localizations hydrolyze phytic acid present in cells. The specificity of hydrolysis of phytic acid by alkaline phytase from lily (Lilium longiflorum L.) pollen is described. Structures of the intermediate inositol phosphates and the final product were established by a variety of nuclear magnetic resonance techniques (1H-, 31P-, and 31P-1H-detected multiple quantum coherence spectroscopy, and total correlation spectroscopy). On the basis of the structures identified we have proposed a scheme of hydrolysis of phytic acid. Initial hydrolysis of the phosphate ester occurs at the D-5 position of phytic acid to yield the symmetrical I-1,2,3,4,6-P5. The two subsequent dephosphorylations occur adjacent to the D-5 hydroxyl group to yield I-1,2,3-P3 as the final product. Alkaline phytase differs from other phytases in the specificity of hydrolysis of phosphate esters on the inositol ring, its high substrate specificity for phytic acid, and biochemical properties such as susceptibility to activation by calcium and inhibition by fluoride. The physiological significance of alkaline phytase and the biological role of I-1,2,3-P3 remain to be identified.
植酸酶是负责水解植酸（肌醇-1,2,3,4,5,6-六磷酸，即I-1,2,3,4,5,6-P6）的主要酶类。多种具有不同特异性、性质和定位的植酸酶可水解细胞中存在的植酸。本文描述了来自百合（Lilium longiflorum L.）花粉的碱性植酸酶对植酸的水解特异性。通过多种核磁共振技术（1H-、31P-和31P-1H检测的多量子相干光谱以及全相关光谱）确定了中间肌醇磷酸酯和最终产物的结构。基于所鉴定的结构，我们提出了植酸的水解方案。磷酸酯的初始水解发生在植酸的D-5位，生成对称的I-1,2,3,4,6-P5。随后的两次去磷酸化发生在与D-5羟基相邻的位置，生成I-1,2,3-P3作为最终产物。碱性植酸酶在肌醇环上磷酸酯水解的特异性、对植酸的高底物特异性以及诸如对钙激活和氟抑制的敏感性等生化特性方面与其他植酸酶不同。碱性植酸酶的生理意义和I-1,2,3-P3的生物学作用仍有待确定。
