An intracellular aminopeptidase N synthesized by Pseudomonas putida Lup was purified and characterized. The approx. 150-fold purified enzyme showed highest activity against A-β-naphthylamide at pH 7.5 and at temperature 40°C and was 100% thermostable for 240 min at 40°C. P. putida lup aminopeptidase N is a monomer with molecular mass approx. 99 kDa determined by SDS-PAGE and gel permeation chromatography. The enzyme has broad substrate specificity, but is the most active against protein substrates with N-terminal alanine and arginine. The activity of P. putida Lup aminopeptidase N is strongly inhibited in the presence of specific metallopeptidase inhibitors and is partly recovered in the presence of Zn²⁺ and Co²⁺ ions. Co²⁺, Mg²⁺ and Ca²⁺ ions increased the activity of the enzyme. Moreover, the enzyme was inhibited by inhibitors of cysteine enzymes. Analysis of fragments of the amino acid sequence of the purified enzyme demonstrated high similarity to PepN of Pseudomonas putida GB-1.
Oxidative DNA damage and DNA repair may mediate several cellular processes, like replication and transcription, mutagenesis and apoptosis and thus may be important for the organism development as well as its pathogenesis, including cancer. Activity of DNA repair enzymes can depend on many factors, such as gene polymorphism, mRNA and protein level, as well as enzymes activation and inhibition. Modulation of base excision repair pathway eliminating from DNA oxidatively formed lesions may be caused by the diet, inflammation and neoplastic transformation. Reactive oxygen species and some diet components induce transcription of several Base Excision Repair enzymes, e.g. major human AP-endonuclease, (APE1) and 8-oxoG-DNA glycosylase (OGG1). The carcinogenic process in human lungs decreases repair activity for 8-oxoG in transcription independent manner, but increases repair activity of eA and eC, as measured in tumors and unchanged lung tissues of lung cancer patients. Thus, modulation of repair enzymes activities may be a cell response on their way to differentiation or neoplastic transformation.