HUMAN GROWTH-HORMONE ADSORPTION-KINETICS AND CONFORMATION ON SELF-ASSEMBLED MONOLAYERS

The adsorption process of the recombinant human growth hormone on orga nic films, created by self-assembly of octadecyltrichlorosilane, arach idic acid, and dipalmitoylphosphatidylcholine, is investigated and com pared to adsorption on silica and methylated silica substrates. Inform ation on the adsorption process of human growth hormone (hGH) is obtai ned by using total internal reflection fluorescence (TIRF). The intens ity, spectra, and quenching of the intrinsic fluorescence emitted by t he growth hormone's single tryptophan are monitored and related to ads orption kinetics and protein conformation. For the various alkylated h ydrophobic surfaces with differences in surface density and conformati onal freedom it is observed that the adsorbed amount of growth hormone is relatively large if the alkyl chains are in an ordered structure w hile the amounts adsorbed are considerably lower for adsorption onto l ess ordered alkyl chains of fatty acid and phospholipid layers. Adsorp tion on methylated surfaces results in a relatively large conformation al change in the growth hormone's structure, as displayed by a 7 nm bl ue shift in emission wavelength and a large increase in the effectiven ess of fluorescence quenching. Conformational changes are less evident for hGH adsorption onto the fatty acid and phospholipid alkyl chains. Adsorption kinetics on the hydrophilic head groups of the self-assemb led monolayers are similar to those on solid hydrophilic surfaces. The relatively small conformational changes in the hGH structure observed for adsorption on silica are even further reduced for adsorption on f atty acid head groups.