Glycerophosphate 1-phosphate

In the glycerophosphate shuttle, two different glycerophosphate dehydrogenases, one in the cytoplasm and one on the outer face of the mitochondrial inner membrane, work together to carry electrons into the mitochondrial matrix (Figure 21.32). NADH produced in the cytosol transfers its electrons to dihydroxyaeetone phosphate, thus reducing it to glyeerol-3-phosphate. This metabolite is reoxidized by the FAD -dependent mitochondrial membrane enzyme to... 

FIGURE 21.33 The glycerophosphate shuttle (also known as the glycerol phosphate shuttle) couples the cytosolic oxidation of NADH with mitochondrial reduction of [FAD]. 

Alkaline phosphatase catalyzes the dephosphorylation of a mmber of artificial substrates ( ) including 3-glycerophosphate, phenylphosphate, p-nitrophenylphosphate, thymolphthalein phosphate, and phenolphthalein phosphate. In addition, as shown recently for bacterial and human enzymes, alkaline phosphatase simultaneously catalyzes the transphosphorylation of a suitable substance which accepts the phosphoryl radical, thereby preventing the accumulation of phosphate in the reaction mediim (25). 

Acid phosphatase catalyzes the dephosphorylation of an artificial organic substrate, such as B-glycerophosphate, phenyl-phosphate or thymolphthalein monophosphate. The analyst may measure either the phosphate or the organic radical liberated. 

Aldolase 4.1.2.3 C Fructose-1,6-diphosphate NADH Glyceraldehyde-3- phosphate Glycerophosphate dehydrogenase... 

A different application of visible microscopy was pioneered by Gomori. In 1941 he showed that alkaline phosphatase could be specifically located by its hydrolysis of soluble phosphate esters (initially glycerophosphate). If calcium ions were present in the medium in which the sections were incubated, insoluble calcium phosphate precipitated as a result of the action of the hydrolase. The site of the precipitate could be visualized if cobalt or lead salts were subsequently added to replace calcium and the sections exposed to hydrogen sulfide. In principle many hydrolases and other enzymes could be studied using the appropriate substrates and precipitants. It was important to ensure that the products of the enzyme reactions did not diffuse from the sites where the enzymes were located. It was also essential that the reagents could reach the enzyme site. 

This enzyme [EC 2.7.8.5] (also referred to as phosphati-dylglycerophosphate synthase, glycerophosphate phos-phatidyltransferase, and 3-phosphatidyl-l -glycerol-3 -phosphate synthase) catalyzes the reaction of CDP-diac-ylglycerol with glycerol 3-phosphate to produce CMP and 3-(3-phosphatidyl)glycerol 1-phosphate. 

DHAP can be prepared by oxidation of L-glycerol-3-phosphate (L- G3P) catalyzed by glycerophosphate oxidase, coupled with hydrogen peroxide decomposition in the presence of catalase (Scheme 4.5) [14]. More recently, this synthetic route has... 

Chronic in vivo hemolysis produces serum lactic dehydrogenase elevations in patients with mitral or atrial valve cardiac prosthesis (J2). In a series of 11 such patients these increases ranged from 1.1 to 1.6 times the upper limit of normal (S29). Blood pH is altered in hemolyzcd specimens because carbonic anhydrase is liberated from the erythrocytes and presumably alters the distribution of H2CO3 and NaHCOs (B2). Hemolysis will effect acid phosphatase activity if the substrate is hydrolyzed by erythrocyte acid phosphatase. Thus, hemolysis would be of concern if phenyl phosphate was the substrate, but would have a negligible effect if )8-glycerophosphate, which is not hydrolyzed by red cell acid phosphatase, was used (Bl). 

Liquid oral tonic preparations containing glycerophosphates and/or other phosphates and/or central nervous system stimulant and such preparations containing alchohol more than 20 proof. 

Various calcium sails and organic compounds lull into this category of dietary supplements and are frequently used in feeds and foods. Some of the more Important additives include calcium carbonate, calcium glycerophosphate, calcium phosphate (di- and monobasic), calcium pyrophosphate, calcium sulfate, and calcium pantothenate. 

In an early review, Kay listed a number of phosphate derivatives that were hydrolyzed by bone phosphatase 34). These included hexose phosphates, glycerophosphates, ethyl phosphate, adenylate, and phenyl phosphate. It was thought that PP(—which had a much lower pH optimum—was also hydrolyzed by the same enzyme. Phosphodiesters were regarded at best as poor substrates and possibly were not substrates at all. By 1936 it was evident that the situation was more complex than had originally been thought (35). The existence of different classes of phosphatases was recognized some, such as hexosediphosphatase 109), were much more specific than others, and it appeared that one tissue could contain several different kinds of phosphatase. Kidney extracts,... 

Perhaps the most characteristic feature of alkaline phosphatase is the way in which the pH optimum changes with increasing substrate concentration. A typical set of curves for calf intestinal phosphatase and phenyl phosphate is given in Fig. 1. Other examples of this type of behavior are found with -glycerophosphate and chicken intestinal... 

With different aryl phosphates at a fixed substrate concentration an analogous set of curves is generated (155). A correlation between the second dissociation constant of the ester and the pH optimum, rate of hydrolysis, and Km value was noted With increasing pK of the substrate, the pH optimum became more neutral, the rate of hydrolysis decreased, and Km increased. With rat intestinal phosphatase and / -glycerophosphate a linear relationship was found between the logarithm of the substrate concentration and the pH optimum (158) and has since been confirmed for tissue phosphatases of several mammalian species and of poultry (156). 

Figure 1 (38) illustrates that maximal hydrolysis of phenyl phosphate occurred at pH 4.9, 5.0, and 5.0 in acetate, citrate, and tris-HCl buffers, respectively. For p-nitrophenyl phosphate, the corresponding values were 4.9, 4.7, and 5.5. For / -glycerophosphate, the values were 5.5, 5.7, and... 

Fig. 1. Prostatic acid phosphatase activity as a function of pH ( ) phenyl phosphate (O) p-nitrophenyl phosphate and (A) /8-glycerophosphate. Buffers Ac, acetate Cit, citrate and tris. From Nigam et al. (88).

Figure 2 (38) shows that the effect of temperature on reaction rate was quite similar for phenyl and p-nitrophenyl phosphate and altogether different for /3-glycerophosphate. 

Relative Rates of Hydrolysis of a- and /3-Glycerophosphates and Phenyl Phosphate by the Acid Phosphatases of the Prostate and Red Cells 1... 

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