Measurement of serum alkaline phosphatase

Alkaline phosphatase is a commonly requested enzyme test in clinical chemistry. However, the enzyme is not particularly substrate specific, which has led to a proliferation of methods for its analysis. It can exhibit a variable instability effect depending on the techniques required for its storage or analysis. Methods can also be highly dependent on sample isoenzyme distribution and reagent purity, leading to problems in the quality control of its analysis and in the comparison of results obtained from different methods. Alkaline phosphatase is not tissue specific and this may on occasion lead to uncertainty in the interpretation of its measured activity in blood serum. In recent years there has been a number of attempts to standardize methodology for this and other enzymes. Perhaps an alternative approach to the measurement of alkaline phosphatase activity will alleviate some of the problems encountered.     

Determination of covalently bound myo-inositol in bovine erythrocyte acetylcholinesterase and porcine kidney alkaline phosphatase

Bovine erythrocyte acetylcholinesterase and porcine kidney alkaline phosphatase were purified to a homogeneous state. By using gas chromatography-mass spectrometry, we demonstrated the presence of covalently bound myo-inositol in these purified enzymes. The quantitative data suggest that one molecule of myo-inositol is bound to each subunit of these enzyme proteins. The covalently bound inositol was removed from these enzyme molecules by deamination with nitrous acid, suggesting the possibility that myo-inositol is directly bound to amino sugar.     

Intestinal alkaline phosphatase-like properties of horse kidney alkaline phosphatase

Two isoenzymes of alkaline phosphatase from horse kidney were identified by cellulose acetate electrophoresis. Horse kidney alkaline phosphatase was similar to horse intestinal alkaline phosphatase, in regard to both antigenicity and response to levamisole inhibition, but different from horse liver alkaline phosphatase. This study suggests that horse kidney alkaline phosphatase is an expression of the intestinal gene locus and not the hepatic gene locus.     

Human kidney and urinary alkaline phosphatases

1. Four fractions of kidney alkaline phosphatase were prepared by chromatography on DEAE-Sephadex. An investigation of their properties suggests that the fractions represent modifications of a single kidney enzyme. 2. Urinary alkaline phosphatase resembles kidney enzyme in most of its properties, but differs in K(m) and in the degree by which it is activated by Mg(2+) ions. 3. Estimates of the molecular weights of kidney and urinary alkaline phosphatase gave values of 150000-170000 for kidney phosphatase and 75000 for the urinary enzyme. 4. It is suggested that urinary alkaline phosphatase is a sub-unit of kidney phosphatase, but it has not been possible to simulate the formation of urinary enzyme by treating kidney enzyme with urea or H(+) ions.     

Characterization of alkaline phosphatase in canine serum

On the basis of carbohydrate structure, normal dog serum contains three basic types of serum alkaline phosphatase (SAP) corresponding to (1) highly branched complex (non-concanavalin A-binding), (2) complex, or (3) high-mannose (both concanavalin A-binding) oligosaccharide structures. Subsequent binding experiments with monoclonal antibody to intestinal alkaline phosphatase (AP) and bromotetramisole inhibition studies clearly indicated the presence of intestinal-like SAP. Concanavalin A (Con-A) binding characteristics suggested the presence of a bone-like SAP. Con-A-binding and isoelectric focusing results revealed the presence of two (type Ib and IIb) major SAP isoenzymes thought to be of hepatic origin. SAP isoenzymes appear to be modified when compared to tissue AP, particularly in regard to molecular size and, in some cases, carbohydrate structure.     

Cloning and sequencing of bovine kidney alkaline phosphatase cDNA

The molecular cloning and nucleotide sequencing of bovine kidney alkaline phosphatase is reported. The homology with the human enzyme is about 90% at both the nucleotide and amino acid levels. The only significant sequence differences occur at the respective C termini. The high degree of homology also extends into the 5' and 3' untranslated regions of the two cDNAs.     

Catalytic properties of alkaline phosphatase from pig kidney

The enzymic properties of alkaline phosphatase (EC 3.1.3.1) from pig kidney brush-border membranes were studied. 1. It hydrolyses ortho- and pyro-phosphate esters, the rate limiting step (V(max.)) being independent of the substrate. It transphosphorylates to Tris at concentrations above 0.1m-Tris. 2. The pH optimum for hydrolysis was between 9.8 and 10. The pK of the enzyme-substrate complex is 8.7 for p-nitrophenyl phosphate and beta-glycerophosphate. Excess of substrate inhibits the enzymic activity with decreasing pH. The pK of the substrate-inhibited enzyme-substrate complex, 8.7, is very similar to that for the enzyme-substrate complex. The pK values of the free enzyme appear to be 8.7 and 7.9. 3. Inactivation studies suggest that there is an essential tyrosine residue at the active centre of the enzyme. 4. The energy of activation (E) and the heat of activation (DeltaH) at pH9.5 showed a transition at 24.8 degrees C that was unaffected by Mg(2+). 5. Kinetic and atomic-absorption analysis indicated the essential role of two Zn(2+) ions/tetrameric enzyme for an ordered association of the monomers. Zn(2+) in excess and other bivalent ions compete for a second site with Mg(2+). Mg(2+) enhances only the rate-limiting step of substrate hydrolysis. 6. Amino acid inhibition studies classified the pig kidney enzyme as an intermediate type of previously described alkaline phosphatases. It has more similarity with the enzyme from liver and bone than with that from placenta.