Kinetic comparison of tissue non-specific and placental human alkaline phosphatases expressed in baculovirus infected cells: application to screening for Down's syndrome.
BACKGROUND
In humans, there are four alkaline phosphatases, and each form exhibits a characteristic pattern of tissue distribution. The availability of an easy method to reveal their activity has resulted in large amount of data reporting correlations between variations in activity and illnesses. For example, alkaline phosphatase from neutrophils of mothers pregnant with a trisomy 21 fetus (Down's syndrome) displays significant differences both in its biochemical and immunological properties, and in its affinity for some specific inhibitors.


RESULTS
To analyse these differences, the biochemical characteristics of two isozymes (non specific and placental alkaline phosphatases) were expressed in baculovirus infected cells. Comparative analysis of the two proteins allowed us to estimate the kinetic constants of denaturation and sensitivity to two inhibitors (L-p-bromotetramisole and thiophosphate), allowing better discrimination between the two enzymes. These parameters were then used to estimate the ratio of the two isoenzymes in neutrophils of pregnant mothers with or without a trisomy 21 fetus. It appeared that the placental isozyme represented 13% of the total activity of neutrophils of non pregnant women. This proportion did not significantly increase with normal pregnancy. By contrast, in pregnancies with trisomy 21 fetus, the proportion reached 60-80% of activity.


CONCLUSIONS
Over-expression of the placental isozyme compared with the tissue-nonspecific form in neutrophils of mother with a trisomy 21 fetus may explain why the characteristics of the alkaline phosphatase in these cells is different from normal. Application of this knowledge could improve the potential of using alkaline phosphatase measurements to screen for Down's syndrome.
Denier
Colette C
CC
Laboratoire de Synthèse et Physicochimie de Molécules d'Intérêt Biologique, Université Paul Sabatier (UMR 5068), 118 route de Narbonne, 31 062, Toulouse, France. denier@cict.fr
Brisson-Lougarre
Andrée A
AA
Biasini
Ghislaine G
GG
Grozdea
Jean J
JJ
Fournier
Didier D
DD
D000469:Alkaline Phosphatase / Q000032:analysis* / Q000235:genetics / Q000378:metabolism; D016367:Baculoviridae / Q000235:genetics; D004796:Clinical Enzyme Tests; D004314:Down Syndrome / Q000175:diagnosis; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000494:pharmacology; D004795:Enzyme Stability; D005260:Female; D058851:GPI-Linked Proteins; D006801:Humans; D007527:Isoenzymes / Q000032:analysis* / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D009504:Neutrophils / Q000201:enzymology; D009596:Nitrophenols / Q000737:chemistry / Q000378:metabolism; D009943:Organophosphorus Compounds / Q000737:chemistry / Q000378:metabolism; D010710:Phosphates / Q000737:chemistry / Q000494:pharmacology; D010920:Placenta / Q000201:enzymology*; D011247:Pregnancy; D011489:Protein Denaturation; D013773:Tetramisole / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology
D004791:Enzyme Inhibitors; D058851:GPI-Linked Proteins; D007527:Isoenzymes; D009596:Nitrophenols; D009943:Organophosphorus Compounds; D010710:Phosphates; C008644:nitrophenylphosphate; C006226:4-bromotetramisole; D013773:Tetramisole; D000469:Alkaline Phosphatase; C019839:alkaline phosphatase, placental; C035638:thiophosphoric acid