Interaction of human growth hormone and human erythrocyte membranes studies by intrinsic fluorescence.

The intrinsic fluorescence of human erythrocyte membranes excited by unpolarized and polarized light has been studied with and without the addition of human growth hormone. The peak emission intensity of the membranes appeared at 332 nm, with a distinct shoulder at about 303 nm. Excitation spectra contained two peaks, at 282 and 225 nm. Fluorescence polarization was maximal (about 0.4) near 295 nm and decreased to approximately 0.18 near 225 nm. In the presence of 1 x 10(-15) M human growth hormone, or 70 molecules per membrane (1.45 x 10(-6) cm(2)), there was about a 20% decrease in peak membrane fluorescence. This occurred maximally with excitation at 282 and 225 nm, with little difference with excitation at 295 nm. Human growth hormone also decreased the fluorescence polarization from 0.34 to 0.25. The growth hormone effect was optimal at 37 degrees C and pH 7.4. No effect was noted at pH 6.0 or 8.0. Bovine growth hormone or bovine serum albumin was without effect. A biologically active fragment from a tryptic digest of bovine growth hormone produced effects on membrane fluorescence similar to human growth hormone. The data are consistent with the proposition that human growth hormone, by some cooperative mechanism, produces a conformational change in the membrane proteins with associated depolarization of fluorescence.