Current Enzyme Inhibition - Volume 7, Issue 2, 2011

Glutathione is abundant in the lining fluid that bathes the gas exchange surface of the lung. On the one hand glutathione in this extracellular pool functions in antioxidant defense to protect cells and proteins in the alveolar space from oxidant injury; on the other hand, it functions as a source of cysteine to maintain cellular glutathione and protein synthesis. These seemingly opposing functions are regulated through metabolism by gamma-glutamyl transferase (GGT, EC 2.3.2.2). Even under normal physiologic conditions, lung lining fluid (LLF) contains a concentrated pool of GGT activity exceeding that of whole lung by about 7-fold and indicating increased turnover of glutathione at the epithelial surface of the lung. With oxidant stress LLF GGT activity is amplified even further as glutathione turnover is accelerated to meet the increased demands of cells for cysteine. Mouse models of GGT deficiency confirmed this biological role of LLF GGT activity and revealed the robust expansiveness and antioxidant capacity of the LLF glutathione pool in the absence of metabolism. Acivicin, an irreversible inhibitor of GGT, can be utilized to augment LLF fluid glutathione content in normal mice and novel GGT inhibitors have now been defined that provide advantages over acivicin. Inhibiting LLF GGT activity is a novel strategy to selectively augment the extracellular LLF glutathione pool. The enhanced antioxidant capacity can maintain lung epithelial cell integrity and barrier function under oxidant stress.

Isoprenoid compounds constitute an immensely diverse group of acyclic, monocyclic and polycyclic compounds that play important roles in all living organisms. Despite the diversity of their structures, this plethora of natural products arises from only two 5-carbon precursors, isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP). This review will discuss the enzymes in the mevalonate (MVA) and methylerythritol phosphate (MEP) biosynthetic pathways leading to IPP and DMAPP with a particular focus on MEP synthase (DXR) and IPP isomerase (IDI), which are potential targets for the development of antibiotic compounds. DXR is the second enzyme in the MEP pathway and the only one for which inhibitors with antimicrobial activity at pharmaceutically relevant concentrations are known. All of the published DXR inhibitors are fosmidomycin analogues, except for a few bisphosphonates with moderate inhibitory activity. These far, there are no other candidates that target DXR. IDI was first identified and characterised over 40 years ago (IDI-1) and a second convergently evolved isoform (IDI-2) was discovered in 2001. IDI-1 is a metalloprotein found in Eukarya and many species of Bacteria. Its mechanism has been extensively studied. In contrast, IDI-2 requires reduced flavin mononucleotide as a cofactor. The mechanism of action for IDI-2 is less well defined. This review will describe how lead inhibitors are being improved by structure-based drug design and enzymatic assays against DXR to lead to new drug families and how mechanistic probes are being used to address questions about the mechanisms of the isomerases.

Fungi can cause life-threatening diseases, particularly in patients with weakened immunological systems. Although treatment options are available for these individuals, dose-limiting toxicity and the appearance of drug-resistant microorganisms are growing problems. Detailed structural and functional characterization of fungal proteases has led to novel insights into the workings of these fascinating catalytic machines. Identification and characterization of proteasemediated processes in human pathogenic fungi is progressing at a rapid rate. In these microorganisms, aspartic-type proteases carry out “housekeeping” tasks common to many eukaryotes as well as functions highly specific to the fungal life cycles. Consequently, the possibility of developing selective inhibitors of key aspartic proteases of pathogenic fungi into novel chemotherapeutic strategies is being vigorously explored. The present review describes the knowledge in the area of aspartic proteases produced by human fungal pathogens. As well, the effects of aspartic proteolytic inhibitors on multiple vital processes of fungal cells, with special emphasis on their roles to arrest fungal development and virulence, will be presented and discussed.

Carbonic anhydrases (EC 4.2.1.1) are ubiquitous metalloenzymes present in prokaryotes and eukaryotes that are encoded by five evolutionarily unrelated gene families involved in numerous physiological and pathological processes. Novel interesting chemo types, in addition to the sulfonamide and sulfamate were discovered, many of which are based on natural products, such as phenols/polyphenols, phenolic acids, and coumarins. Methanolic extract of Abrus precatorius belongs to family Fabaceae tested for human carbonic anhydrase (hCA) I and II inhibition study. The significant IC 50 values are calculated for the methanolic extract of Abrus precatorius for hCA I found to be 0.13 mM/ml which is showing relatively less potent inhibition than hCA against hCA II having IC 50 values of 0.12 mM/ml. Abrus precatorius is a weak inhibitor that may constitute leads for developing tighter binding compounds.

Pathogenic yeasts of the genus Candida represent a serious threat to immunocompromised individuals. Soluble secreted aspartic proteinases produced by these opportunistic pathogens have been studied as one of the virulence factors and potential target for therapeutic intervention. Several structures of these enzymes in complex with inhibitors have been published; however, only a limited number of novel inhibitory compounds have been reported recently. Other members of aspartic proteinase family received less attention, although they are important for Candida survival in the host environment. Proteinases attached to the cell surface by GPI-anchor, as well as vacuolar aspartic proteinases may thus become promising therapeutic targets. This review summarizes the data available on less studied aspartic proteinases of C. albicans, and poses the question, whether the knowledge of vacuolar and GPI-anchored aspartic proteinases from Saccharomyces cerevisiae can inspire design of compounds inhibiting these types of enzymes in the pathogenic yeasts.

Soluble as well as agarose immobilized pumpkin urease was utilized for easy and rapid detection and quantitation of fluoride in aqueous solution. Pumpkin urease was immobilized in 1.5 % agarose leading to 74.2 % immobilization. Inhibition by both soluble and agarose immobilized enzyme revealed a clear dependence on concentration and time. In order to inhibit the activity completely in soluble enzyme, 45 mM fluoride was required while agarose immobilized enzyme required almost double the concentration of the inhibitor i.e., 80 mM. The inhibition caused by fluoride was noncompetitive with Ki value of 3.9 and 2.3 mM. The significance of the observations is discussed.