Investigations on the primary effect of uv-irradiation: importance of free radicals for the uv-inactivation of enzymes

Book · Mon Jan 01 04:00:00 EST 1973

OSTI ID:4319263

Nemec, H W

From fourth scientific meeting of the Deutsche Gesellschaft fer Medizinische Physik eV; Homburg, Germany (4 Oct 1973). A method for the uv irradiation of enzyme suspensions is described that allows a simple determination of the energy absorbed by the enzyme. The uv irradiation of trypsin in oxygen- free suspensions yields results similar to irradiation under vacuum. Longlived free radicals were detected in trypsin by means of ESR spectroscopy after irradiation at 278 K. The unpaired electrons are mainly located at the C/sub alpha / atoms of the polypeptide chain and at sulfur atoms of the cystine residue. Apart from the ESR measurements, the decrease in the enzymatic activity was investigated, as well as the quantum yield for the radical formation and the inactivation. The low amount of 0.07 radicals per inactivated molecule seems to indicate that the long-lived free radicals themselves have no effect on the inactivation of the enzyme but rather point to the fact that damage has already occurred. An anslysis of these radicals, however, allows conclusions to be made on the extent of the radiation effect, as an increasing yield of sulfur radicals goes hand in hand with an increased inactivation quantum yield. Both radiation effects are mainly associated with the formation of primary sulfur radicals. Different transfer mechanisms are assumed to induce the formation of secondary sulfur radicals of the type RS' from the primary radicals. From the present results it can be concluded that the disulphide break is of particular importance for the inactivation. This disulphide break can be caused by the absorption by the cystine residues and above all by the quanta absorbed by the tryptophane residues. Another possible conclusion is that reactions leading to the formation of cross bonds lake part in enzyme inactivation. (GE)

• Research Organization: Univ., Freiburg, Ger.
• NSA Number: NSA-29-018560
• OSTI ID: 4319263
• Country of Publication: Germany
• Language: German

Related Subjects

*ENZYMES-- CHEMICAL RADIATION EFFECTS
*TRYPSIN-- CHEMICAL RADIATION EFFECTS
BIOCHEMISTRY
CHEMICAL BONDS
ELECTRON SPIN RESONANCE
IN VITRO
INACTIVATION
IRRADIATION
LIFETIME
N48110* --Life Sciences--Radiation Effects on Biochemicals-- In-Vitro
PHOTON BEAMS
POLYPEPTIDES
RADICALS
RADIOINDUCTION
RADIOLYSIS
ULTRAVIOLET RADIATION