Phosphate function

Long-chain polyisoprenoid. molecules with a terminal alcohol moiety are called, polyprenols. The dolichols, one class of polyprenols (Figure 8.18), consist of 16 to 22 isoprene units and, in the form of dolichyl phosphates, function to carry carbohydrate units in the biosynthesis of glycoproteins in animals. Polyprenyl groups serve to anchor certain proteins to biological membranes (discussed in Chapter 9). 

Many models were proposed to account for the coupling of electron transport and ATP synthesis. A persuasive model, advanced by E. C. Slater in 1953, proposed that energy derived from electron transport was stored in a high-energy intermediate (symbolized as X P). This chemical species—in essence an activated form of phosphate—functioned according to certain relations according to Equations (21.22)-(21.25) (see below) to drive ATP synthesis. 

Fowle et al. (2000) have measured the sorption by a soil bacterium (B. subtilis) of uranyl in 0.1 M NaC104 at 25°C as a function of pH, time, and solid solute ratio, using a batch technique. The stoichiometiy and thermodynamic stability of the important uranyl-surface complexes indicated that uranyl formed two different surface complexes, one involving neutral phosphate functional groups, and another with deprotonated carboxyl functional groups, on the bacterial cell wall ... 

Scheme 6.1 Glycosyl phosphates functioning as glycosl donors.

Scheme 6.2 a-Diaryl phosphate and cyclic (3-phosphate functioning as glycosyl donors. 

Scheme 6.5 Glycosyl phosphates functioning as glycosyl donors in P-selective formation of...

A nucleotide consists of a nitrogenous base linked to a monosaccharide linked to a phosphate functional group. 

Vitamin B6 is a collective term for pyridoxine, pyridoxal, and pyridox amine, all derivatives of pyridine. They differ only in the nature of the functional group attached to the ring (Figure 28.10). Pyridoxine occurs primarily in plants, whereas pyridoxal and pyridoxamine are found in foods obtained from animals. All three compounds can serve as precur sors of the biologically active coenzyme, pyridoxal phosphate. Pyridoxal phosphate functions as a coenzyme for a large number of enzymes, par ticularly those that catalyze reactions involving amino acids. 

Glycerate-3-phosphate, glycerate-2-phosphate, and phos-phoenolpyruvate (PEP) make up another equilibrium group of metabolites that, like the hexose phosphates or the triose phosphates, function as a single metabolic pool (see fig. 12.13). 

The undecaprenol phosphate functions as a carrier and is acted upon by the series of reactions. 

The chemistry and biological activities of lipid A are reviewed in earlier chapters of this volume. As noted there, the components of the lipid A complexes from Salmonella species and j5. coli are derivatives of a disaccharide comprised of two D-glucosamine units linked B,l->-6. The disaccharide is substituted at positions 1 and 4 by phosphate functions and on the amino nitrogens by B-hydroxymyristoyl groups. A variable number (up to 5) of ester-linked fatty acyl residues is also present. In the simplest components the phosphates are present as monoester groups. 

To carry out the convergent synthesis in its purest form, one would use building blocks Q.0 and. ) having protected phosphate groups already in place. After coupling the only further operations required would be removal of the protecting groups from position 3 and from the phosphate functions. 

Resistant to acids and bases and without a tendency to migrate, this group is stable for all the reactions employed in the synthesis of oligonucleotides. It is photolytically cleaved under a controlled pH without affecting the pyrimidine or purine bases [107, 108]. It has also been used as a photoremovable protecting group for the phosphate function [109]. 

In addition, esters of dextran-bearing palmitoyl groups and phosphate functions can be used for the preparation of specifically modified liposomes, which are exploited for the entrapment of peptides such as hirudin, the most potent inhibitor of thrombin [105]. 

Pyridoxal phosphate functions as a co actor in enzymes involved in transamination reactions required for the S5mthesis and catabolism of the amino acids. 

Third, including the phospholipid, all GPI anchors contain two or more phosphate moieties. Because of the concern of potential chemical incompatibility, the vast majority of reported GPI syntheses have adopted a strategy in which the phosphate functionalities are introduced at the final stage of the synthesis (O Scheme 2). 

Pyridoxal-5 phosphate (P-5 -P) and its amino analogue, pyridoxamine-5 -phosphate, function as coenzymes in the amino-transfer reactions. The P-5 -P is bound to the apoen-zyme and serves as a true prosthetic group. The P-5 -P bound to the apoenzyme accepts the amino group from the first substrate, aspartate or alanine, to form enzyme-bound pyridoxamine-5 -phosphate and the first reaction product, oxaloacetate or pyruvate, respectively. The coenzyme in amino form then transfers its amino group to the second substrate, 2-oxoglutarate, to form the second product, glutamate. P-5 -P is thus regenerated. 

Interest in phosphorus-containing calixarenes continues. Structures reported include hexa(diethoxyphosphoryloxy)calix[6]arene (8), inherently chiral 1,2-bridged calix[4]arene diphosphates, and a calixarene like C3 symmetric receptor with a phosphate function at the cavity bottom. " The purification of phosphate substituted calixarenes has been studied by chiral HPLC and by normal reverse phase HPLC. Mono(6-0-diphenoxyphosphoryl)-P-cyclodextrin (9) and mono(6-0-ethoxyhydroxyphosphoryl)-p-cyclodextrin (10) have been synthesised and show enantioselective inclusion of D and L amino acids e.g. 3.6 for D/L serine in the case of 9). ... 

---