Rennie P S, Bruchovsky N, McLoughlin M G, Batzold F H, Dunstan-Adams E E
J Steroid Biochem. 1983 Jul;19(1A):169-73.
Kinetic parameters (KM and Vmax) of the 5 alpha-reductase activities in homogenates of stroma and epithelium, isolated from BPH tissue, were determined using both testosterone and progesterone as substrate. The mean KM values for stromal 5 alpha-reductase, at 67.9 nM and 27.7 nM for testosterone and progesterone respectively, were 3-4-fold higher than the comparable KM estimates for the epithelial enzyme. The KM estimates for the epithelial 5 alpha-reductase showed little variation whereas those measured in the stromal homogenates could be subgrouped at less than 50 nM and greater than 100 nM. The mean Vmax for the stromal 5 alpha-reductase was approximately 235 pmol/30 min/mg protein irrespective of the substrate used; a value 10-fold higher than the Vmax of the epithelial 5 alpha-reductase. Preliminary experiments with inhibitors of 5 alpha-reductase demonstrated that the stromal and epithelial enzymes differed in their relative sensitivity to these compounds. Three major conclusions can be drawn from these results: first, that progesterone is a better substrate for prostatic 5 alpha-reductase than testosterone; second, that BPH tissue has at least two isoenzymes of 5 alpha-reductase--one in the epithelium and one (or more) in the stroma; and third, in hyperplastic prostates, most of the 5 alpha-reductase molecules are located in the stroma.
以睾酮和孕酮作为底物，测定了从良性前列腺增生（BPH）组织分离出的基质和上皮匀浆中5α-还原酶活性的动力学参数（米氏常数KM和最大反应速度Vmax）。基质5α-还原酶的平均KM值，睾酮为67.9 nM，孕酮为27.7 nM，分别比上皮酶的相应KM估计值高3至4倍。上皮5α-还原酶的KM估计值变化不大，而在基质匀浆中测得的值可分为小于50 nM和大于100 nM两组。无论使用何种底物，基质5α-还原酶的平均Vmax约为235 pmol/30 min/mg蛋白质；该值比上皮5α-还原酶的Vmax高10倍。5α-还原酶抑制剂的初步实验表明，基质酶和上皮酶对这些化合物的相对敏感性不同。从这些结果可以得出三个主要结论：第一，孕酮是前列腺5α-还原酶比睾酮更好的底物；第二，BPH组织至少有两种5α-还原酶同工酶——一种在上皮中，一种（或多种）在基质中；第三，在增生性前列腺中，大多数5α-还原酶分子位于基质中。
