KM Ratio (km + ratio)

Distribution by Scientific Domains

Selected Abstracts

Phosphorus-limited growth dynamics in two Baltic Sea cyanobacteria, Nodularia sp. and Aphanizomenon sp.

Jenny Degerholm
Abstract Rates of carbon (C) specific growth and nitrogen (N2) fixation were monitored in cultures of Baltic Sea Nodularia and Aphanizomenon exposed to gradual limitation by inorganic phosphorus (P). Both cyanobacteria responded by decreased cellular P content followed by lowered rates of growth and N2 fixation. C-specific growth and cellular N content changed faster in Aphanizomenon both when inorganic P was lowered as well as during reintroduction of P. Aphanizomenon also showed a more rapid increase in N-specific N2 fixation associated with increased C-specific growth. When ambient concentrations of inorganic P declined, both cyanobacteria displayed higher rates of alkaline phosphatase (APase) activity. Lower substrate half-saturation constants (KM) and higher Vmax : KM ratio of the APase enzyme associated with Nodularia suggest a higher affinity for dissolved organic P (DOP) substrate than Aphanizomenon. Aphanizomenon, which appears more sensitive to changes in ambient dissolved inorganic P, may be adapted to environments with elevated concentrations of P or repeated intrusions of nutrient-rich water. Nodularia on the other hand, with its higher tolerance to increased P starvation may have an ecological advantage in stratified surface waters of the Baltic Sea during periods of low P availability. [source]

Purification and properties of trypsin-like enzyme from the midgut of Morimus funereus (coleoptera, cerambycidae) Larvae

Nikola Lon
Abstract Trypsin-like enzyme (TLE) from the anterior midgut of Morimus funereus larvae was purified by anion exchange chromatography and gel filtration chromatography and characterized. Specific TLE activity was increased 322-fold by purification of the crude midgut extract. The purified enzyme had a pH optimum of 9.0 (optimum pH range 8.5,9.5) and temperature optimum of 45°C with the KM ratio of 0.065,mM for benzoyl-arginine- p -nitroanilide (BApNA). Among a number of inhibitors tested, the most efficient was benzamidine (KI value of 0.012,mM, Ic50 value of 0.204,mM) while inhibition of TLE activity by SBTI, TLCK, and PMSF was partial. Almost all divalent cations tested enhanced the enzyme activity, amongst them Co2+ and Mn2+ stimulated TLE activity for 2.5 times. The purified TLE (after gel-filtration on Superose 12 column) had a molecular mass of 37.5,kDa with an isoelectric point over 9.3. Sodium dodecylsulphate-polyacrylamide gel electrophoresis (SDS-PAGE) revealed one band of 38,kDa, suggesting that the enzyme is a monomer. © 2010 Wiley Periodicals, Inc. [source]

Enhancement of coenzyme binding by a single point mutation at the coenzyme binding domain of E. coli lactaldehyde dehydrogenase

José Salud Rodríguez-Zavala
Abstract Phenylacetaldehyde dehydrogenase (PAD) and lactaldehyde dehydrogenase (ALD) share some structural and kinetic properties. One difference is that PAD can use NAD+ and NADP+, whereas ALD only uses NAD+. An acidic residue has been involved in the exclusion of NADP+ from the active site in pyridine nucleotide-dependent dehydrogenases. However, other factors may participate in NADP+ exclusion. In the present work, analysis of the sequence of the region involved in coenzyme binding showed that residue F180 of ALD might participate in coenzyme specificity. Interestingly, F180T mutation rendered an enzyme (ALD-F180T) with the ability to use NADP+. This enzyme showed an activity of 0.87 ,mol/(min * mg) and Km for NADP+ of 78 ,M. Furthermore, ALD-F180T exhibited a 16-fold increase in the Vm/Km ratio with NAD+ as the coenzyme, from 12.8 to 211. This increase in catalytic efficiency was due to a diminution in Km for NAD+ from 47 to 7 ,M and a higher Vm from 0.51 to 1.48 ,mol/(min * mg). In addition, an increased Kd for NADH from 175 (wild-type) to 460 ,M (mutant) indicates a faster product release and possibly a change in the rate-limiting step. For wild-type ALD it is described that the rate-limiting step is shared between deacylation and coenzyme dissociation. In contrast, in the present report the rate-limiting step in ALD-F180T was determined to be exclusively deacylation. In conclusion, residue F180 participates in the exclusion of NADP+ from the coenzyme binding site and disturbs the binding of NAD+. [source]

Some properties of polyphenol oxidase from lily

Ying Yang
Summary A study of crude polyphenol oxidase (PPO) from lily bulbs was carried out to provide information useful for guiding food processing operations. Optimum pH for the enzyme activity in the presence of catechol, were 4.0 and 7.0 at room temperature(approximately 20 °C) and the enzyme was stable in the pH range from 5.0 to 6.5 at 4 °C for 10 h. Its optimum temperature was 40 °C and the heat inactivation of the enzyme followed first-order kinetics. Lily PPO possessed a diphenolase activity toward catechol, catechin and gallic acid; catechin was the best substrate for the enzyme considering the Vmax/Km ratio. The most effective enzyme inhibitor was sodium sulphite, although ascorbic acid, l -cysteine and thiourea were also effective inhibitors at high concentration. But NaCl and citric acid were poor inhibitors of the enzyme. Data generated by this study might help to better prevent lily bulbs browning. [source]

Maintenance of the alcohol dehydrogenase polymorphism in Tiger Salamanders, II.

Differences in biochemical function among allozymes
Abstract 1.,Previous studies of Tiger Salamanders demonstrated that variation in alcohol dehydrogenase (Adh) contributed significantly to associations between multilocus heterozygosity and oxygen consumption traits, and that Adh variation was associated with levels of pond-oxygen and metamorphic ability in extreme oxygen environments. Here Adh allozymes are characterized kinetically, and relationships between Adh and oxygen-related physiological traits (ATP/Hb, 2,3-DPG/Hb) are measured. 2.,Kinetic differences were measured among Adh allozymes in the acetaldehyde-to-ethanol direction: kcat/Km ratios (the catalytic constant divided by the Michaelis,Menton constant) were significantly higher in Adh-SF than the other two genotypes, and in Adh-SS compared with Adh-FF. No significant differences were measured in the ethanol to acetaldehyde direction. 3.,Adh-SS had a significantly higher ATP/Hb than Adh-FF, with the Adh-SF intermediate. In addition, a significant interaction between Hb and body mass was measured, such that Adh-FF showed a negative relationship between Hb concentration and body mass while the other two genotypes showed a positive relationship. 4.,These results are consistent with the hypothesis that variation at the Adh locus has adaptive and physiological significance, and that functional differences among Adh allozymes partly explain significant associations between multilocus genotype and organismal traits. [source]