Proximity Iodo-labeling of Human Cervical Mucus with an Endogenous Peroxidase

A calcium-dependent guaiacol peroxidase (GPx) was detected in the cervix and cervical mucus. Daily measurements of cervical mucus GPx can predict the day of ovulation by 4-5 days, since GPx activity drops significantly as 17beta-estradiol levels peak before ovulation. After ovulation, the concomitant rise of progesterone and GPx mark the end of the optimal time for conception. Cervical mucus was radiolabeled with hydrogen peroxide and Na125I, instead of guaiacol, to detect proteins iodinated by GPx in the follicular and luteal phases of the menstrual cycle. Based on the promising preliminary results, I describe the use of the non-radioactive Na127I and mass spectrometry to detect iodinated peptides and identify the autoiodinated GPx protein and its nearest neighbors. Among them enzymes and signaling proteins will help untie the Gordian knot of multicomponent protein complexes and transient interactions coordinated in the cervix during ovulatory menstrual cycles. Future studies could reveal whether different iodinated mucus proteins and their expression levels are associated with clinical symptoms and conditions during the menstrual cycle prompting research for new markers and therapy targets.