Drosophila as a model to study the genetic mechanisms of obesity-associated heart dysfunction

Obesity and cardiovascular disease are among the world's leading causes of death, especially in Western countries where consumption of high caloric food is commonly accompanied by low physical activity. This lifestyle often leads to energy imbalance, obesity, diabetes and their associated metabolic disorders, including cardiovascular diseases. It has become increasingly recognized that obesity and cardiovascular disease are metabolically linked, and a better understanding of this relationship requires that we uncover the fundamental genetic mechanisms controlling obesity-related heart dysfunction, a goal that has been difficult to achieve in higher organisms with intricate metabolic complexity. However, the high degree of evolutionary conservation of genes and signalling pathways allows researchers to use lower animal models such as Drosophila, which is the simplest genetic model with a heart, to uncover the mechanistic basis of obesity-related heart disease and its likely relevance to humans. Here, we discuss recent advances made by using the power of the Drosophila as a powerful model to investigate the genetic pathways by which a high fat diet may lead to heart dysfunction.     

Physiological and biochemical characteristics of poly gamma-glutamate synthetase complex of Bacillus subtilis.

An enzymatic system for poly gamma-glutamate (PGA) synthesis in Bacillus subtilis, the PgsBCA system, was investigated. The gene-disruption experiment showed that the enzymatic system was the sole machinery of PGA synthesis in B. subtilis. We succeeded in achieving the enzymatic synthesis of elongated PGAs with the cell membrane of the Escherichia coli clone producing PgsBCA in the presence of ATP and D-glutamate. The enzyme preparation solubilized from the membrane with 8 mM Chaps catalyzed ADP-forming ATP hydrolysis only in the presence of glutamate; the D-enantiomer was the best cosubstrate, followed by the L-enantiomer. Each component of the system, PgsB, PgsC, and PgsA, was translated in vitro and the glutamate-dependent ATPase reaction was kinetically analyzed. The PGA synthetase complex, PgsBCA, was suggested to be an atypical amide ligase.     

Preparation of stereoselectively-deuterated NADH and NADPH by coupling of glutamate racemase and glutamate dehydrogenase

Summary We have developed a simple method for preparation of [4R²H] and [4S-²H]-NAD(P)H by combination of glutamate racemase, glutamate dehydrogenase, and 2-aminoethanesulfonate: 2-oxoglutarate aminotransferase. In this new enzymatic procedure, no deuterated substrates were used.     

Overproduction of glutamate racemase of Pediococcus pentosaceus in Escherichia coli clone cells and its purification

We previously isolated a 6.0-kb DNA fragment that specifies glutamate racemase activity from the chromosomal DNA of Pediococcus pentosaceus by digestion with HindIII (N. Nakajima, K. Tanizawa, H. Tanaka, and K. Soda, 1986), Agric. Biol. Chem. 50, 2823-2830). We digested it further with EcoRI to obtain a fragment of 1.8 kb, which was blunt-ended and ligated into the SmaI site of vector plasmid pKK223-3. The recombinant plasmid showed a high glutamate racemase activity upon transformation of Escherichia coli W3110 cells with it; the plasmid was named pICR223. Glutamate racemase was overproduced in the clone cells and occurred in inclusion bodies in the cells. The enzyme was solubilized with 6 M urea, renatured by dialysis to remove urea, and purified to homogeneity with an overall yield of about 70% after a single DEAE-cellulose column chromatography. The amount of enzyme produced by the clone cells corresponded to about 38% of the total insoluble protein.     

Alanine racemase of alfalfa seedlings (Medicago sativa L.): first evidence for the presence of an amino acid racemase in plants

We demonstrated several kinds of D-amino acids in plant seedlings, and moreover alanine racemase (E.C.5.1.1.1) in alfalfa (Medicago sativa L.) seedlings. This is the first evidence for the presence of amino acid racemase in plant. The enzyme was effectively induced by the addition of L- or D-alanine, and we highly purified the enzyme to show enzymological properties. The enzyme exclusively catalyzed racemization of L- and D-alanine. The K(m) and V(max) values of enzyme for L-alanine were 29.6 x 10(-3) M and 1.02 mol/s/kg, and those for D-alanine are 12.0 x 10(-3) M and 0.44 mol/s/kg, respectively. The K(eq) value was estimated to be about 1 and indicated that the enzyme catalyzes a typical racemization of both enantiomers of alanine. The enzyme was inactivated by hydroxylamine, phenylhydrazine and some other pyridoxal 5'-phosphate enzyme inhibitors. Accordingly, the enzyme required pyridoxal 5'-phosphate as a coenzyme, and enzymologically resembled bacterial alanine racemases studied so far.     

Mechanism of reactions catalyzed by selenocysteine beta-lyase

The reaction mechanism of selenocystine beta-lyase has been studied and it was found that elemental selenium is released enzymatically from selenocysteine, and reduced to H2Se nonenzymatically with dithiothreitol or some other reductants that are added to prepare selenocysteine from selenocystine in the anaerobic reaction system. 1H and 13C NMR spectra of L-alanine formed in 2H2O have shown that an equimolar amount of [beta-2H1]- and [beta-2H2]alanines are produced. The deuterium isotope effect at the alpha position was observed; kH/kD = 2.4. These results indicated that the alpha hydrogen of selenocysteine was removed by a base at the active site, and was incorporated into the alpha position of alanine, a product, without exchange of a solvent deuterium. When the enzyme was incubated with L-selenocysteine in the absence of added pyridoxal 5'-phosphate, the activity decreased with prolonged incubation time. However, the activity was recovered by addition of 5'-phosphate. The spectrophotometric study showed that the inactivated enzyme was the apo form. The apoenzyme was activated by a combination of pyridoxamine 5'-phosphate and various alpha-keto acids such as alpha-ketoglutarate and pyruvate. Thus, the enzyme is inactivated through transamination between selenocysteine and the bound pyridoxal 5'-phosphate to produce pyridoxamine 5'-phosphate and a keto acid derived from selenocysteine. The pyridoxal enzyme, an active form, is regenerated by addition of alpha-keto acids. This regulatory mechanism is analogous to those of aspartate beta-decarboxylase [EC 4.1.1.12], arginine racemase [EC 5.1.1.9], and kynureninase [EC 3.7.1.3] [K. Soda and K. Tanizawa (1979) Adv. Enzymol. 49, 1].     

Acceleration of cheese ripening with liposome-entrapped proteinase

Summary Rulactine, a proteinase used for the acceleration of cheese ripening, was entrapped in three types of liposomes and these were added to Saint-Paulin cheese type manufacturing milk. Enzyme entrapment rates ranged from 3 to 9% according to the type of liposomes and liposome retention rates in cheese curd from 35 to 65%. An electrophoretic study of protein breakdown in the cheeses gave correlative data.     

Microbial assimilation of alkyl nitro compounds and formation of nitrite

66 representative strains of bacteria, yeasts and fungi were tested for their ability to grow in a semidefined medium containing 0.5% nitroethane as a nitrogen source. About half of them were found capable of growing in the medium. Hansenula beijerinckii, Candida utilis, and Penicillium chrysogenum were most active in assimilating nitroethane. 2-Nitropropane inhibited growth of most of the microorganisms tested in a medium containing 0.2% peptone and 0.2% glycerol. Hansenula mrakii was found to grow rapidly in the nitroethane-peptone medium after a lag phase. Nitrite was accumulated in the culture fluid after the phase of logarithmic multiplication, and increased with increase of the growth, followed by a decline after the maximum growth. The alkyl nitro compounds were oxidatively denitrified to form nitrite by the crude enzyme from Hansenula mrakii. Nitroethane was generally a poor substrate, but was the best inducer to produce the nitro compounds oxidizing enzyme. 2-Nitropropane and nitroethane were enzymatically oxidized to and acetone and acetaldehyde, respectively, which were isolated as 2,4-dinitrophenylhydrazones and identified. Nitrite formed was found to be reduced into ammonia by the intact cells and also the crude enzyme.