Steroid 21-sulfatase activity in human placenta

Area of Science:

• Biochemistry
• Endocrinology
• Reproductive Biology

Background:

• Deoxycorticosterone sulfate (DOCS) is abundant in fetal plasma.
• DOCS is not metabolized via deoxycorticosterone (DOC) in non-pregnant humans, suggesting low steroid 21-sulfatase activity.
• Hydrolysis of DOCS has been observed in the human placenta.

Purpose of the Study:

• To investigate the presence and characteristics of steroid 21-sulfatase activity in human placenta.
• To determine if placental steroid 21-sulfatase can hydrolyze fetal DOCS.

Main Methods:

• Preparation of microsome-enriched fractions from human placental tissue.
• Assay of steroid 21-sulfatase activity using [3H]-deoxycorticosterone sulfate.
• Determination of enzyme kinetics, including Michaelis constant (KM).

Main Results:

• Steroid 21-sulfatase activity was detected in human placental microsomes.
• Reaction conditions were optimized for linearity with time and protein concentration.
• The apparent KM for deoxycorticosterone sulfate was determined to be 100 microM.

Conclusions:

• Human placenta possesses active steroid 21-sulfatase.
• Placental hydrolysis of fetal DOCS could lead to DOC secretion into maternal circulation.
• This placental pathway may contribute to high maternal DOC levels in late pregnancy.