Structural phosphate
Editor-In-Chief: Henry A. Hoff
Overview
Inside a cell, phosphate may be structural to a nucleic acid such as DNA and RNA or phospholipid. Outside the cell, phosphate may be dissolved in extracellular fluid (ECF) or form structures such as bone and teeth. Bringing phosphate in any form into the cell from a phosphate containing structure or for such a structure and when needed transporting phosphate out of the cell perhaps to a structure is a necessary activity of phosphate homeostasis for that cell.
Introduction
Inorganic phosphate (Pi) (structural phosphate) behaves as a serine phosphate and is not the same as the enzyme-bound phosphate (catalytic phosphate) derived from ATP during a catalytic reaction.[1]
Catalytic phosphate
Inorganic phosphate (Pi) (structural phosphate) behaves as a serine phosphate and is not the same as the enzyme-bound phosphate (catalytic phosphate) derived from ATP during a lyase reaction of EC 4.1.3.8.[1] Evidence indicates that EC 4.1.3.8 contains one structural phosphate for each catalytic phosphate, which does not affect its catalytic activity.[1] The γ phosphate of ATP is the catalytic phosphate. EC 4.1.3.8 ATP citrate lyase contains acid-labile, catalytic phosphate after the enzyme is reacted with ATP and Mg2+, whereas the structural phosphate is acid-stable, base-labile.[2] There are 2 mol of acid-labile catalytic phosphate and 2 mol of base-labile structural phosphate per tetramer. The pH 7.5 buffer contained concentrations of ADP, Pi, and free Mg2+ similar to those found in vivo.[2] Glucagon induces an incorporation of acid-stable phosphate into ATP citrate lyase without a concomitant change in enzyme activity.[2]
Intracellular structural phosphate
In the mathematical modeling of cell growth and phosphatase biosynthesis it is necessary to determine the intracellular concentration of structural phosphate.[3]
Nucleotides
Analysis of the phosphate moiety present in mononucleotides (NMP) can allow the identification of structural phosphate binding motifs.[4]
When nucleotide hydrolysis is coupled to the polymerization process, the two ends of the polymer behave differently, and the critical concentration required for assembly at one end is different from that required for the opposite end. However, NTP hydrolysis is usually associated but not directly coupled with polymerization. When there are NTP-bound subunits at the ends, the polymer is stable and continues to grow slowly. When at the polymer ends there are subunits containing NDP, the polymer is in a shrinking phase, depolymerizes rapidly and completely, and much faster at lower mer concentrations.
Microfilaments
During the assembly of actin into microfilaments, actin-ATP becomes actin ADP upon polymerization.
Microtubules
Pi, BeF3 or AIF4, structural phosphate analogs, have a stabilizing effect on microtubules containing GDP tubulin.[5] The structural phosphate of microtubules is the GDP in the interior of the polymer.
Phospholipid
Nucleic acid
Cartilage
Teeth
Hydroxyapatite, which is a crystalline calcium phosphate is the primary mineral of enamel.[6]
By weight, seventy percent of dentin consists of the mineral, hydroxylapatite, twenty percent is organic material, and ten percent is water.[7]
Cementum is a specialized bony substance covering the root of a tooth, composed of approximately 45% inorganic material (mainly hydroxyapatite), 33% organic material (mainly collagen) and 22% water.
Bone
During bone resorption high levels of phosphate are released into the ECF as osteoclasts tunnel into mineralized bone, breaking it down and releasing phosphate, that results in a transfer of phosphate from bone fluid to the blood. During childhood, bone formation exceeds resorption, but as the aging process occurs, resorption exceeds formation.
Transphosphorylation between nucleotides and hydroxyapatite (HA) results in a pyrophosphate on HA that is distinctive from pyrophosphate absorbed onto HA from solution. This may be due to a different orientation of the pyrophosphate on the surface depending on the origin of the pyrophosphate.[8]
References
- ↑ 1.0 1.1 1.2 Linn TC, Srere PA (1979). "Identification of ATP citrate lyase as a phosphoprotein". J Biol Chem. 254 (5): 1691–8. PMID 762167. Unknown parameter
|month=ignored (help) - ↑ 2.0 2.1 2.2 Janski AM, Srere PA, Cornell NW, Veech RL (1979). "Phosphorylation of ATP Citrate Lyase in Response to Glucagon". J Biol Chem. 254 (19): 9365–8. PMID 489538. Unknown parameter
|month=ignored (help) - ↑ Toda K, Yabe I (2004). "Mathematical model of cell growth and phosphatase biosynthesis in Saccharomyces carlsbergensis under phosphate limitation". Biotech Bioeng. 21 (3): 487–502. doi:10.1002/bit.260210310. Unknown parameter
|month=ignored (help) - ↑ "Conserved Positions for Ribose Recognition: Importance of Water Bridging Interactions Among ATP, ADP and FAD-protein Complexes". J Mol Biol. 323 (3): 523–32. 2002. doi:10.1016/S0022-2836(02)00975-0. Unknown parameter
|month=ignored (help) - ↑ Avila J (1990). "Microtubule dynamics". FASEB J. 4 (15): 3284–90. PMID 2253844. Unknown parameter
|month=ignored (help) - ↑ Johnson, Clarke (1998). "Biology of the Human Dentition".
- ↑ Cate, A.R. Ten. (1998). Oral Histology: development, structure, and function (5th ed.). pp. 150–5. ISBN 0-8151-2952-1.
- ↑ Taves DR, Reedy RC (1969). "A structural basis for the transphosphorylation of nucleotides with hydroxyapatite". Calcified Tissue International. 3 (1): 284–92. doi:10.1007/BF02058670. Unknown parameter
|month=ignored (help)