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The physical characteristics and enzymatic modification of fetal intestinal alkaline phosphatase in amniotic fluid
Insights
Amniotic fluid alkaline phosphatase shares intestinal enzyme traits but differs in mobility and size. Bromelain digestion yields a smaller form, similar to a cancer-related isoenzyme.
Area of Science:
- Biochemistry
- Perinatal Medicine
Background:
- Alkaline phosphatase (ALP) exists in various isoenzyme forms.
- Intestinal ALP is found in fetal and adult small intestines.
- Specific ALP isoenzymes can be biomarkers in certain conditions.
Purpose of the Study:
- To characterize the alkaline phosphatase (ALP) in amniotic fluid during mid-gestation.
- To compare amniotic fluid ALP with intestinal ALP found in neonates and adults.
- To investigate the structural properties and potential origins of amniotic fluid ALP.
Main Methods:
- Electrophoretic analysis in polyacrylamide gel.
- Molecular weight determination.
- Enzymatic digestion with bromelain.
Main Results:
- Amniotic fluid ALP at 16-18 weeks gestation exhibits inhibition patterns similar to intestinal isoenzymes.
- This enzyme shows low electrophoretic mobility and high molecular weight in amniotic fluid.
- Bromelain digestion reduces the molecular weight of amniotic fluid ALP, creating a form comparable in size to the Kasahara isoenzyme found in cancer patients.
Conclusions:
- Amniotic fluid ALP during mid-gestation is predominantly an intestinal-type isoenzyme.
- Its distinct electrophoretic and molecular properties suggest a unique structural form or post-translational modification.
- The similarity to the Kasahara isoenzyme hints at a potential link to fetal intestinal ALP re-expression, possibly relevant in pathological states.
Abstract:
The predominant form of alkaline phosphatase in amniotic fluid at 16 to 18 weeks gestation has the inhibition characteristics of the isoenzymes from adult and fetal small intestine. These characteristics are shared by an alkaline phosphatase of presumed intestinal origin occasionally found in the sera of premature neonates. However, in contrast to the rapid anodal migration of the latter enzyme, amniotic fluid phosphatase is of low electrophoretic mobility in polyacrylamide gel, and it has a high molecular weight. Digestion of amniotic fluid with bromelain produces a rapidly-migrating active enzyme form, with a molecular weight of about 135,000, compared with 145,000 for the fetal intestinal phosphatase in serum. The bromelain-treated amniotic fluid phosphatase is similar in size to a Kasahara isoenzyme in the serum of a cancer patient, which is itself thought to result from re-expression of a fetal intestinal phosphatase gene.