THE SUBCELLULAR DISTRIBUTION OF 17β-HYDROXYSTEROID DEHYDROGENASE IN THE HUMAN TERM PLACENTA

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Abstract
Human term placenta tissue homogenates were subjected to differential centrifugation procedures. The composition of the subcellular fractions was monitored with a number of marker enzymes and the effectiveness of these enzyme systems was evaluated. The subcellular fractions were tested for their 17.beta.-hydroxy dehydrogenase activity on testosterone, estradiol and the synthetic substrate retrotestosterone. Buffer medium composition showed a direct influence upon enzyme distribution patterns of all fractions during the same differential centrifugation procedure. All enzyme activities tested became less sedimentable when glycerol was present in the fractionation buffer. Glycerol stabilized soluble 17.beta.-hydroxy dehydrogenase activity during fractionation. The activity of steroid-converting enzymes was inhibited by the presence of glycerol in the medium. Subcellular distribution of marker enzymes did not sustain the presence of mitochondrial 17.beta.-hydroxy dehydrogenase but related it to microsomal contamination. The proportion of 17.beta.-hydroxy dehydrogenase activity in the particulate fractions showed a decrease in the substrate order retrotestosterone > testosterone > estradiol which was independent from the buffer medium used. Specific activities for both particle-bound and soluble 17.beta.-hydroxy dehydrogenase increased in the substrate order retrotestosterone < testosterone < estradiol. The particulate enzyme activity was maximal with NAD+ for the 3 substrates tested, but in the cytosol fraction NADP+ was the preferential co-enzyme only when estradiol was used as the substrate.