PLP

The graph of n/n against plp° will thus be obtained as the difference between the two hyperbolae represented by the equations... 

Because of the large difference in tp between successive molecular layers, each layer becomes complete at a relative pressure (plp°)g which is determined by the value of rp/kT for that layer, viz integral values). Each layer will therefore give rise to a step, such that the riser corresponds to the cooperative build-up of the layer and the tread to the transition between the layer and the next higher one. 

Plictran Plioflex Plot plan PLP-DPG-PLP Plug valves Plumbic acetate Plumbing applications PlumbopaHadimte Plumbostanmte Plumbous acetate Plume containment Plummer s disease Plums... 

Prolactin-Like Proteins. A number of prolactin-like proteins (PLPs), which ate distinct from the PLs, have been identified in mminants and rodents (11,23). Several cDNA transcripts coding for PLPs in catde have been identified (23). These transcripts code for proteins which possess about 40% sequence homology with bovine PRL 60% if conservative substitutions ate considered. Three glycosylated PLPs, ie, PLP-A, -B, and -C, ate produced during pregnancy in the rat (11). Two additional prolactin-related molecules have been identified in the mouse (24,25), ie, proliferin [92769-12-5] (PLF) and PLF-related protein [98724-27-7]. These ate not found in other rodents and may be unique to the mouse. The functional roles of PLPs remain to be deterrnined. 

Pyridoxal Derivatives. Various aldehydes of pyridoxal (Table 3) react with hemoglobin at sites that can be somewhat controlled by the state of oxygenation (36,59). It is thereby possible to achieve derivatives having a wide range of functional properties. The reaction, shown for PLP in Figure 3, involves first the formation of a Schiff s base between the amino groups of hemoglobin and the aldehyde(s) of the pyridoxal compound, followed by reduction of the Schiff s base with sodium borohydride, to yield a covalendy-linked pyridoxyl derivative in the form of a secondary amine. 

Fig. 3. (a) Reaction of pytidoxal 5 -phosphate (PLP) witii an amino-temiinal amino group of hemoglobin (Hb). The reagent is in the form of a Schiff s base with tris(hydroxymethyl)aminomethane [77-86-1] (Tris) buffet, and the reaction is a transamination, (b) The resulting unstable Schiff s base is reduced with... 

Table 5. Properties of Pyridoxylated Polymerized Hemoglobin (PLP-polyHb) ...

Most of the criteria found in literature are extracted from Bowen et al. (1968). Diagrams of pressure versus duration are presented for various body positions in relation to the blast wave, from which the chance of survivability can be calculated. Those diagrams were combined in a pressure-impulse diagram, which is depicted in Figure C-1. The scaled overpressure P equals Plp, in which P is the actual pressure acting on the body, and po is the ambient pressure. The scaled impulse i equals ... 

Carbonic anhydrase Pyridoxal phosphate (PLP) Amino groups Aspartate aminotransferase... 

FIGURE 15.15 (a) The structure of a glycogen phosphorylase monomer, showing the locations of the catalytic site, the PLP cofactor site, the allosteric effector site, the glycogen storage site, the tower helix (residnes 262 throngh 278), and the snbnnit interface. 

The biologically active form of vitamin Bg is pyridoxal-5-phosphate (PEP), a coenzyme that exists under physiological conditions in two tautomeric forms (Figure 18.25). PLP participates in the catalysis of a wide variety of reactions involving amino acids, including transaminations, a- and /3-decarboxylations, /3- and ") eliminations, racemizations, and aldol reactions (Figure 18.26). Note that these reactions include cleavage of any of the bonds to the amino acid alpha carbon, as well as several bonds in the side chain. The remarkably versatile chemistry of PLP is due to its ability to... 

FIGURE 25.25 Biosynthesis of sphingolipids in animals begins with the 3-ketosphinga-nine synthase reaction, a PLP-dependent condensation of palmitoyl-CoA and serine. Subsequent rednction of the keto group, acylation, and desatnration (via rednction of an electron acceptor, X) form ceramide, the precnrsor of other sphingolipids. 

The amino acid methionine is biosynthesized by a multistep roule that includes reaction of an inline of pyridoxal phosphate (PLP) to give an unsaturated imine. which then reacts with cysteine. What kinds of reactions are occurring in the two steps ... 

Most amino acids lose their nitrogen atom by a transamination reaction in which the -NH2 group of the amino acid changes places with the keto group of ct-ketoglutarate. The products are a new a-keto acid plus glutamate. The overall process occurs in two parts, is catalyzed by aminotransferase enzymes, and involves participation of the coenzyme pyridoxal phosphate (PLP), a derivative of pyridoxine (vitamin UJ. Different aminotransferases differ in their specificity for amino acids, but the mechanism remains the same. 

The mechanism of the first part of transamination is shown in Figure 29.14. The process begins with reaction between the a-amino acid and pyridoxal phosphate, which is covalently bonded to the aminotransferase by an iminc linkage between the side-chain -NTI2 group of a lysine residue and the PLP aldehyde group. Deprotonation/reprotonation of the PLP-amino acid imine in steps 2 and 3 effects tautomerization of the imine C=N bond, and hydrolysis of the tautomerized imine in step 4 gives an -keto acid plus pyridoxamine... 

Step 1 of Figure 29.14 Transimination The first step in transamination is trans-imination—the reaction of the PLP—enzyme imine with an a-amino acid to give a PLP—amino acid imine plus expelled enzyme as the leaving group. The reaction occurs by nucleophilic addition of the amino acid -NH2 group to the C=N bond of the PLP imine, much as an amine adds to the C=0 bond of a ketone or aldehyde in a nucleophilic addition reaction (Section 19.8). The pro-tonated diamine intermediate undergoes a proton transfer and expels the lysine amino group in the enzyme to complete the step. 

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