Isolation and photo-oxidation of lysozyme fragments

Abstract

Reduction of the four disulfide bonds and further carboxymethylation of lysozyme followed by its reaction with CNBr brings about L-I, (aa 1-12) and L-II-III (aa 13-129) peptides. When breaking the polypeptidic chain by CNBr action and freeing the peptides formed through S-S bonds reduction and carboxymethylation three peptides are obtained corresponding to L-I (aa 1-12), L-II (aa 13-105) and L-III (aa 106-129). L-II-III, L-III and L-II peptides were separately subjected to photo-oxidation in presence of riboflavin, in 0.05 M phosphate buffer, pH 7.0. The kinetic analysis of Trp photo-oxidation in L-II-III peptides shows that these residues keep, to a great extent, the degree of exposition they had in native lysozyme. L-II peptide also presents Trp residues with a different degree of exposition. Presence of Tyr photo-oxidation in L-II and L-II-III peptides - what does not take place in native lysozyme - suggests a relationship between photo-oxidation selectivity and the degree of exposition of certain amino acid residues in spatial configuration.

A common bicyclic protein kinase cascade inactivates the regulatory enzymes of fatty acid and cholesterol biosynthesis

“…These protein kinases include a cyclic AMP-independent protein kinase which we have recently partially purified from rat liver [ 1 l] and which we have tentatively termed acetyl-CoA carboxylase kinase-3 (ACK3). HMG-CoA reductase is also inactivated by multiple protein kinases [ 121, including a protein kinase which is stimulated by phosphorylation [ 13,141, and an AMPstimulated protein kinase [15,16]. It has not been clear whether these latter two HMG-CoA reductase kinases are distinct enzymes.…”