Leukocyte alkaline phosphatase: another organ-specific alkaline phosphatase

Kinetics and characteristics of bovine neutrophil alkaline phosphatase during acute Escherichia coli mastitis

Alkaline phosphatase activity of isolated bovine blood neutrophils was investigated before and during experimentally induced Escherichia coli mastitis. Activities markedly increased 1 wk after infection in neutrophils of cows suffering from moderate or from severe disease. Elevated neutrophil alkaline phosphatase activity did not correlate with a specific stage of maturating postmitotic neutrophils appearing in circulation during mastitis. Neutrophil alkaline phosphatase from healthy cows before infection and from mastitic cows was characterized by means of thermostability, specific inhibitor patterns, slab gel electrophoresis, and kinetic parameter analysis. The leukocyte enzyme from healthy and mastitic cows displayed very similar characteristics, suggesting that the increase in activity during mastitis is most probably related to the enhanced expression of the normal alkaline phosphatase enzyme.

Nuclear localization and characterization of alkaline phosphatase in neutrophils from normal controls and pregnant women

There were controversial data concerning localization of alkaline phosphatase (AP) in neutrophil nuclei under physiological conditions. In this context, the AP pattern has been determined on nuclei preparations from normal human neutrophils. Blood cells were isolated from 10 healthy adults and from 3 women in the third trimester of an uncomplicated pregnancy. Purity of nuclear suspension was checked by electron microscopy and assay of organelle marker enzymes. Electron microscope cytochemistry and immunocytochemistry studies were carried out on WBC. Enzyme characterization was performed by the usual biochemical procedures. AP was found in nuclear preparations from four of ten normal controls. When present, AP was detected in approximately two-thirds of the nuclei examined, representing an average of 20% of the total cell activity. Conversely, a large amount of nucleus-bound enzyme (55% of total AP activity) was recognized in all pregnant women samples. Biochemical and immunological characteristics clearly differentiate AP forms in the two groups of subjects. Normal controls have an heterogeneous enzyme pattern. AP positive preparations contain a mixture of isoenzymes: a prominent heat labile form and a relatively heat stable minor component. The heat stable fraction displays some properties similar to those previously described in leukocyte AP. Pregnant women express a unique very heat labile isoenzyme identical in its main characteristics to the early placental type.

Substrate specificity of alkaline phosphatase from human polymorphonuclear leukocytes

The ability of alkaline phosphatase in purified preparations from human neutrophils and liver to utilize ATP or inorganic pyrophosphate as substrate depended upon the Mg2+ concentration. With pyrophosphate present (1.0 mmol/l), activity peaked at Mg2+ concentrations of 0.25 to 0.50 mmol/l and fell sharply above this. By contrast, p-nitrophenylphosphatase activity was activated with Mg2+ concentration up to 0.75 mmol/l but above this was constant to 5.0 mmol/l. Hydrolysis was abolished by L-levamisole, a specific inhibitor of alkaline phosphatase. Testing butanol extracts of neutrophils from 50 healthy subjects showed good correlation of enzyme activity with p-nitrophenylphosphate and ADP (r = 0.90), and between p-nitrophenylphosphate and pyridoxal phosphate (r = 0.96) as substrate, consistent with hydrolysis of all three phosphoesters by one enzyme. Inhibition studies yielded no evidence of a specific pyridoxal phosphatase. Alkaline phosphatase from human neutrophils has the same broad substrate specificity as other molecular forms of the human enzyme and, like other forms, has little or no activity towards phosphoesters complexed with Mg2+.

Evidence for two isozymes of leukocyte alkaline phosphatase in leukemic leukocytes

Leukocyte alkaline phosphatase (LAP) is a granulocyte enzyme whose level of expression is markedly altered in various disease states. We have characterized LAP from normal cells and leukemic cells with a high level of LAP activity in order to determine whether increased enzyme levels are caused by increased levels of the same enzyme or induction of a different alkaline phosphatase. Leukocyte alkaline phosphatase was purified from normal granulocytes and from leukemic cells of a patient with chronic granulocytic leukemia (CGL) in blast phase with an elevated LAP level. LAP was partially purified utilizing diethylaminoethyl (DEAE)-cellulose ion exchange chromatography, gel filtration, and preparative electrophoresis. The sample prepared from normal granulocytes contained a single protein with LAP activity having a molecular weight of 61,000 as determined by SDS gel electrophoresis. The sample from the CGL blast-phase cells, however, demonstrated two proteins with alkaline phosphatase activity, one with a molecular weight of 61,000 (LAPs) and one with a molecular weight of 45,000 (LAPf). Differential heat inactivation and distinct isoelectric points of the two isozymes suggest that they are different proteins. We interpret our data to suggest two closely related LAP alleles whose expression is controlled independently. This may represent either genetic heterogeneity or induction of "tumor marker" gene expression.

Studies of the biochemical and immunological properties of human neutrophil alkaline phosphatase with comparison to the established alkaline phosphatase isoenzymes

A range of affinity column chromatographic procedures and various inhibitors have been used to compare human neutrophil alkaline phosphatase with the three established isoenzymes. The column chromatography studies have clearly distinguished neutrophil alkaline phosphatase from the intestinal isoenzyme. Inhibition studies with L-phenylalanine, L-homoarginine and levamisole have revealed a distinct pattern of inhibition for liver, kidney and neutrophil alkaline phosphatase which is quite different from the pattern shown by placental and intestinal alkaline phosphatase. Immunospecificity experiments with a monoclonal antibody raised to human liver alkaline phosphatase have shown that it cross reacts with alkaline phosphatase from kidney, bone and neutrophil. In all studies, neutrophil alkaline phosphatase has virtually identical properties to that of liver, kidney and bone alkaline phosphatase. This is strong evidence that neutrophil alkaline phosphatase is a product of the same structural gene which codes for the liver/bone/kidney group of human alkaline phosphatases.