Enzymatic activity unit

The next step in coenzyme M formation is the dephosphorylation of phosphosulfolactate by a Mg(II)-dependent acid phosphatase, ComB. The third enzyme in the pathway, sulfolactate dehydrogenase (ComC), has also been structurally characterized with the bound reaction product NADH. ComC is present in solution as a dimer, and in the crystal the asymmetric unit contains a tetramer of tight dimers. The dimer is the enzymatically active unit and a portion of each monomer binds NADH at the active site. As a result of this interaction, ComC does not contain the classic Rossmann-Fold topology for NADH binding but instead defines a novel fold for NADH binding. 

The advantages of CE for analysis of enzymes are the use of small volumes, versatility, and ability to avoid the extra steps of indicator reactions. We found in some instances, for example, analysis of glutathione transferase it is easier to assign enzymatic activity units (lU) based on the CE because both the substrate and the products can be monitored at the same wavelength. Unfortunately, researchers did not take full advantage of the CE for enzyme analysis. In practice, kinetic spectrophotometric methods remain to be most widely used for routine work while the CE is reserved for those difficult and specialized tests. 

The relative enzymatic activity of each fraction in catalyzing die xandiine dehydrogenase reacdon is cited as arbitrarily defined units. 

Yagi laid the foundation for the enzymology of CODH when he discovered an enzymatic activity in sulfate-reducing bacteria that oxidizes CO to CO2 (118). Twenty-five years later, the first CODH was purified to homogeneity (119, 120). The homogeneous C. thermo-aceticum CODH was shown to contain 2 mol of nickel, 12 iron, 1 zinc, and 14 acid-labile inorganic sulfide per afS dimeric unit (120). 

Dry bean curd refuse was used as the substrate in the lactic acid fermentation with simultaneous saccharification (SSF). The dry bean curd refuse was preliminarily sieved under a mesh size of 250 II m. It contained 12.3% water, 4.0% ash, 0.8% lipid, 29.3% protein, 53.6% carbohydrate, respectively, in weight basis. The cellulase derived from Aspergilltis niger with an enzymatic activity of 25,000 units/g (Tokyo Kasei Industry Inc.) was employed as the saccharification enzyme. 

Enzyme Reference Serums. Several companies sell lyophilized or stabilized reference serums for the calibration of instruments and for quality control. The label values given for the enzymatic activity of these serums should never be taken at face value, as at times they may be quite erroneous (19,33). Also, these values should only be used for the assay with which they were standardized, as interconversion of activity from one method to another for the same enzyme may often lead to marked errors. For instance, it is not recommended that alkaline phosphatase expressed in Bodansky units be multiplied by a factor to convert it to the units of the Ring-Armstrong method, or any other method for that matter. 

The activity of PL was measured [23] from the formation of unsatured oligomers, during pectin degradation (5 g/L) in phosphate-citrate buffer 50 mM, pH 5.6 following the absorbance at 235 nm. The enzymatic activity was expressed as enzymatic units (EU), i.e. amount of enzyme that produces 1 pmol of product per minute. The extinction coefficient (5,550 M" cm was used for calculating product concentration. 

The strains were cultured on Mandels medium + 1% citrus pectin for 5 days and the enzymatic activities of culture filtrates were determined on three substrates citrus pectin, polygalacturonic acid and filter paper, (a) extracellular proteins are in p.g/ml. (b) p>ectinolytic activities on pectin (PC) and on polygalacturonic acid (TO) and Pectin esterase (PE) are in units/ml. (c) total cellulolytic activity (filter paper, fp) are in mg of liberated reducing sugars/ml. 

In regard to the antineoplastic potentials of Rubiaceae, some evidence has already been presented that clearly demonstrates that anthraquinones inhibit the enzymatic activity of topoisomerase II. An example of antineoplastic anthraquinones that target topoisomerase II is mitoxantrone (Novatrone ), which is currently approved for clinical use in the United States (16). In the Pacific Rim, about 150 species of plants classified within the family Rubiaceae are medicinal, of which Prismatomeris albidiflora, Krtoxia valeriartoides, Damnacanthus indicus, and Morinda umbellata are known to produce anthraquinones. An interesting development from Rubiaceae would be to investigate its members for anthraquinones and assess them for topoisomerase inhibitors. The discovery of inhibitors of topoisomerase II of clinical antineoplastic value can be reasonably expected. 

The enzymatic activities of O -chymotrypsin in solution and adsorbed at the different surfaces are presented in Fig. 11, where the specific enzymatic activity (defined as activity per unit mass of protein) is plotted as a function of temperature. The enzyme loses activity due to adsorption. On the hydrophobic Teflon and PS surfaces, the activity is completely gone, whereas on the hydrophilic silica surface, or-chymotrypsin has retained most of its biological function. These differences are in agreement with the adsorption isotherms and the circular dichroism spectra. The influence of the hydrophobicity of the sorbent surface on the affinity of the protein for the sorbent surface, as judged from the rising parts of the adsorption isotherms (Fig. 8), suggests that the proteins are more perturbed and, hence, less biologically active when adsorbed at hydrophobic surfaces. Also, the CD spectra indicate that adsorption-induced structural perturbations are more severe at hydrophobic surfaces. 

With the above design each run is an experiment performed at the settings noted in columns Xj, X2, and X3, with each run having a response (yl - y8). For example, if one were looking for enzymatic activity, the responses yl to y8 would be in units of activity per mg of protein. Notice that for factor A at the low levels (0), the levels for B and C are the same as the levels when A is at its high level (1), i.e. the design... 

It should be noted that the permeability per surface unit of alveolar epithelium per se is not particularly high. The significant absorption found for various substances after pulmonary administration is rather explained by a number of beneficial factors such as the large surface area of the alveoli, the low volume of the epithelial lining fluid, the relatively thin diffusion layer, the absence of mucociliary clearance from the alveoli as well as the limited enzymatic activity in the lining fluids. 

Action. cAMP is an allosteric effector of protein kinase A (PK-A, [3]). in the inactive state, PK-A is a heterotetramer (C2R2), the catalytic subunits of which (C) are blocked by regulatory units (R autoinhibition). When cAMP binds to the regulatory units, the C units separate from the R units and become enzymatically active. Active PK-A phosphorylates serine and threonine residues of more than 100 different proteins, enzymes, and transcription factors, in addition to cAMP, cCMP also acts as a second messenger, it is involved in sight (see p. 358) and in the signal transduction of NO (see p. 388). 

The S-ribonuclease is the complex formed between an eicosapeptide and the S-RNAse. While replacement of various amino acids by fluorinated analogues does not modify the activity of the native complex, replacement of His-12 by 4-F-His has a strong influence. Indeed, the S-ribonuclease, formed between the bovine pancreatic S-RNAse and the fluoro peptide that contains 4-F-His, has no more catalytic activity, but it is stable. This loss of enzymatic activity is probably due to the significant lowering of the pAia of the catalytic His (2.5 units), which results from the presence of the fluorine atom. It is known that histidine plays an important role in nucleophilic and acid-base processes, which are connected to the catalytic activity of numerous enzymes. 

Regulation of histidine synthesis. In all, ten different genes code for the enzymes of histidine biosynthesis in Salmonella typhimurium. They are clustered as the histidine operon, a consecutive series of genes which are transcribed into messenger RNA as a unit.250 251 The gene symbols His A, HisB, etc., are indicated in Fig. 25-13, and their positions on the E. coli gene map are indicated in Fig. 26-4. The gene HisB codes for a complex protein with two different enzymatic activities as shown in Fig. 25-13. 

---