Photoabsorption and Photoelectron Spectra of Enzymes in the Vacuum-uv Region

Abstract

The photoabsorption spectra and photoelectron yield spectra for the enzymes trypsin, ribonuclease, and lysozyme were measured in the vacuum-uv region between 1050 and 2400 angstroms. The energy distribution curves of photoelectrons were also measured. The samples were in the form of thin films on substrates (lithium fluoride plates for photoabsorption measurements and cover glasses coated with gold for photoelectron measurements). The first ionization potentials for these enzymes were determined from the energy distribution curves of photoelectrons. The integral oscillator strengths for wavelengths ranging from 1050 to 2400 angstroms were derived from the absorption spectra: 168 for trypsin, 100 for ribonuclease, and 126 for lysozyme. It is suggested that a considerable part of the absorption spectra for the wavelength region between the first ionization potential and 1050 angstroms in these enzymes may be attributed to the excitations of highly excited states of peptide linkages.