Oonk R B, Grootegoed J A
Department of Biochemistry, Medical Faculty, Erasmus University Rotterdam, The Netherlands.
Mol Cell Endocrinol. 1988 Jan;55(1):33-43. doi: 10.1016/0303-7207(88)90088-3.
Insulin-like growth factor I (IGF-I) binding to cultured Sertoli cells from immature rats was quantitatively evaluated. The binding of 125I-IGF-I to the Sertoli cells was specific, time- and pH-dependent and reversible. Scatchard analysis yielded a Kd of 3.5 X 10(-9) M and a binding capacity of 2080 fmol/mg protein. Competition with IGF-I resulted in a half-maximal displacement by 2 nM IGF-I, whereas insulin up to a concentration of 100 nM gave virtually no displacement of IGF-I binding. Similarly, the gonadotropic hormones follitropin and lutropin did not compete with 125I-IGF-I binding. In previous studies, it was shown that cultured Sertoli cells from immature rats bind insulin with a Kd of 1.8 X 10(-9) M and a binding capacity of 8.5 fmol/mg protein. The binding of IGF-I and insulin to a total testis membrane fraction was studied using testes from immature and adult rats. In testis from 21-day-old rats, the maximal specific binding was relatively high for IGF-I (871 +/- 50 fmol/g wet weight) and relatively low for insulin (118 +/- 11 fmol/g wet weight). In adult testis, the maximal specific binding of IGF-I was 324 +/- 40 fmol/g wet weight and that of insulin was 330 +/- 17 fmol/g wet weight. The binding of IGF-I and insulin expressed as fmol bound per testis was increased 6-fold and 45-fold, respectively, between the age of 21 days and adult age. It is discussed that the numbers of receptors for IGF-I and insulin in testis may be developmentally regulated, and that IGF-I may be more important than insulin with respect to testis development and Sertoli cell maturation in the immature rat.
对胰岛素样生长因子I（IGF-I）与未成熟大鼠培养的支持细胞的结合进行了定量评估。125I-IGF-I与支持细胞的结合具有特异性、时间和pH依赖性且可逆。Scatchard分析得出解离常数（Kd）为3.5×10^(-9) M，结合容量为2080 fmol/mg蛋白质。与IGF-I竞争导致2 nM IGF-I产生半数最大置换，而浓度高达100 nM的胰岛素几乎不引起IGF-I结合的置换。同样，促性腺激素促卵泡素和促黄体素不与125I-IGF-I结合竞争。在先前的研究中，已表明未成熟大鼠培养的支持细胞以1.8×10^(-9) M的Kd和8.5 fmol/mg蛋白质的结合容量结合胰岛素。使用未成熟和成年大鼠的睾丸研究了IGF-I和胰岛素与总睾丸膜部分的结合。在21日龄大鼠的睾丸中，IGF-I的最大特异性结合相对较高（871±50 fmol/g湿重），而胰岛素的相对较低（118±11 fmol/g湿重）。在成年睾丸中，IGF-I的最大特异性结合为324±40 fmol/g湿重，胰岛素为330±17 fmol/g湿重。以每个睾丸结合的fmol表示，IGF-I和胰岛素的结合在21日龄至成年期分别增加了6倍和45倍。讨论了睾丸中IGF-I和胰岛素受体的数量可能受发育调节，并且就未成熟大鼠的睾丸发育和支持细胞成熟而言，IGF-I可能比胰岛素更重要。
