Protein synthetic patterns in immature and mature human oocytes

A preliminary study of protein synthesis and amino acid transport in human oocytes was initiated. Qualitative patterns or protein synthesis were examined in individual oocytes cultured in medium containing radiolabeled methionine. The protein synthetic profile of immature oocytes, resolved by one-dimensional electrophoresis and fluorography, was observed to change markedly following germinal vesicle breakdown and oocyte maturation. No further differences in the one-dimensional protein synthetic patterns were observed in mature oocytes maintained in culture from 10 hours up to as long as 50 hours. The protein synthetic pattern of follicular cells was observed to be distinct from that of oocytes and was characterized by the predominant synthesis of a polypeptide with Mr = 44,000. Based on the specific activity of the methionine precursor, the absolute rate of synthesis was calculated to be about 50 pg protein/oocyte/hour. Total protein content was measured to be about 150 ng/egg. Competition of methionine uptake by leucine, efflux of radiolabeled methionine from preloaded oocytes into medium containing methionine and uptake of methionine in medium with low sodium ion concentration was observed. These findings are consistent with the presence of an L (leucine-preferring) system for neutral amino acid transport, similar to that in mouse and rabbit eggs. These studies provide basic data for further analysis of oocytes and perhaps preimplantation-stage embryos in the future.