Biological characterization of purified native 20-kDa human growth hormone

Because of the propensity of the 20-kDa variant of human growth hormone (GH) to aggregate with itself and with 22-kDa human GH, it has been difficult to prepare monomeric 20-kDa GH in highly purified form. This has been a major complicating factor in determining whether 20-kDa GH has a biological activity profile distinct from that of 22-kDa GH. In the present study, native 20-kDa GH was isolated from a human GH dimer concentrate and purified by a procedure that included column electrophoresis in agarose suspension as a final separation step. This procedure yielded highly purified monomeric 20-kDa GH, which was contaminated to an extent of less than 1% with 22-kDa GH, and which exhibited only a small degree of dimerization upon storage. The native 20-kDa GH was quite active in stimulating growth in hypophysectomized rats, when growth was assessed by body weight gain, longitudinal bone growth, the stimulation of sulfation of cartilage, and the elevation of serum IGF-1 level. However, in all of these growth assays, the 20-kDa GH was somewhat less active than the native 22-kDa GH to which it was compared; e.g., in the body weight gain and longitudinal bone growth assays, it had an estimated potency of 0.6 relative to the 22-kDa GH. The 20-kDa GH exhibited substantial diabetogenic activity when tested for the ability to raise fasting blood glucose concentration and to impair glucose tolerance in ob/ob mice. Also, the native 20-kDa GH had significant in vitro insulin-like activity, although its potency was approximately 20% that of the native 22-kDa GH to which it was compared. Thus, the biological activity profile of native 20-kDa GH differs from that of 22-kDa GH primarily in that insulin-like activity is markedly attenuated.     

31P nuclear magnetic resonance study of the effect of azide on xylose fermentation by Candida tropicalis

Maximal ethanol production by Candida tropicalis grown on xylose was obtained at an oxygen transfer rate of 5 to 7 mmol/liter per h. Addition of 0.2 mM azide increased the ethanol yield by a factor of 3 to 4, based on the cell mass produced, and decreased the formation of the by-product xylitol by 80%. In the presence of azide, ethanol was reassimilated before the carbon source was depleted. At all oxygenation levels studied, azide caused 25 to 60% of the carbon to be lost, most probably as carbon dioxide. Identical spectra were obtained with 31P nuclear magnetic resonance spectroscopy performed on extracts of C. tropicalis grown on xylose in the absence and presence of azide. Azide lowered the levels of sugar phosphates. Enzymatic analysis showed extremely low levels of fructose 1,6-diphosphate compared with the levels obtained in the absence of azide, while the level of malate, a citric acid cycle intermediate, was not influenced by azide. 31P nuclear magnetic resonance spectroscopy performed on xylose-grown whole cells of C. tropicalis showed that azide lowered the intracellular pH, inhibited the uptake of external Pi, and decreased the buildup of polyphosphate in relation to results with untreated cells. Similar results were obtained with the uncoupler of oxidative phosphorylation carbonyl cyanide m-chlorophenylhydrazone (CCCP), except that CCCP treatment led to extremely high levels of internal Pi. The dual effect of azide as a respiratory inhibitor and as an uncoupler is discussed with respect to the metabolism and product formation in xylose-assimilating C. tropicalis.     

Specificity of an HPETE peroxidase from rat PMN

The 15,000xg supernatant of sonicated rat PMN contains 5-lipoxygenase that converts arachidonic acid to 5-hydroperoxyeicosatetraenoic acid (5-HPETE) and leukotriene A4 and an HPETE peroxidase that catalyzes reduction of the 5-HPETE. The specificity of this HPETE peroxidase for peroxides, reducing agents, and inhibitors has been characterized to distinguish this enzyme from other peroxidase activities. In addition to 5-HPETE, the HPETE peroxidase will catalyze reduction of 15-hydroperoxyeicosatetraenoic acid, 13-hydroperoxyoctadecadienoic acid, and 15-hydroperoxy-8,11,13-eicosatrienoic acid, but not cumene or t-butylhydroperoxides. The HPETE peroxidase accepted 5 of 11 thiols tested as reducing agents. However, glutathione is greater than 15 times more effective than any other thiol tested. Other reducing agents, ascorbate, NADH, NADPH, phenol, p-cresol, and homovanillic acid, were not accepted by HPETE peroxidase. This enzyme is not inhibited by 10 mM KCN, 2 mM aspirin, 2 mM salicylic acid, or 0.5 mM indomethacin. When 5-[14C]HPETE is generated from [14C]arachidonic acid in the presence of unlabeled 5-HPETE and the HPETE peroxidase, the 5-[14C]HETE produced is of much lower specific activity than the [14C]arachidonic acid. This indicates that the 5-[14C]HPETE leaves the active site of 5-lipoxygenase and mixes with the unlabeled 5-HPETE in solution prior to reduction and is a kinetic demonstration that 5-lipoxygenase has no peroxidase activity. Specificity for peroxides, reducing agents, and inhibitors differentiates HPETE peroxidase from glutathione peroxidase, phospholipid-hydroperoxide glutathione peroxidase, a 12-HPETE peroxidase, and heme peroxidases. The HPETE peroxidase could be a glutathione S-transferase selective for fatty acid hydroperoxides.     

Characterization of two β-glucosidase genes fromClostridium thermocellum

Summary Two -glucosidase genes, designatedbglA andbglB, were isolated from a gene bank ofClostridium thermocellum DSM 1237. The coding sequences forbglA andbglB were located on non-homologous DNA fragments of 3.2– and 3.4-kb, respectively. Both genes direct inEscherichia coli the synthesis of cytoplasmic -glucosidases, which differ with respect to substrate specificity and temperature profile. The properties of thebglA-encoded -glucosidase A closely resemble that of a -glucosidase previously isolated fromC. thermocellum cultures.     

Rhinovirus 3C protease catalyzes efficient cleavage of a fluorescein-labeled peptide affording a rapid and robust assay.

The 3C protease encoded by human rhinovirus type 2 catalyzes with equal efficiency cleavage of a peptide substrate with or without a fluorescein label attached to the amino acid at the P7' position. Substrates Ac-MEALFQGPLQYKDL-NH2 and MEALFQGPLQYKE(fluorescein)L are hydrolyzed with values of Vmax/KM of 970 M-1 s-1 and 1100 M-1 s-1, respectively. With the labeled substrate, HPLC achieves separation of substrate and product in 2.5 min. Separation in as little as 12 s is feasible. Fluorescein was derivatized so that it could be incorporated into peptides using automated solid-phase peptide synthesis.     

Improved ethanol production from xylose with glucose isomerase and Saccharomyces cerevisiae using the respiratory inhibitor azide

Summary Ethanol was produced from xylose, using the enzyme glucose isomerase (xylose isomerase) and Saccharomyces cerevisiae. The influence of aeration, pH, enzyme concentration, cell mass and the concentration of the respiratory inhibitor sodium azide on the production of ethanol and the formation of by-products was investigated. Anaerobic conditions at pH 6.0, 10 g/l enzyme, 75 g/l dry weight cell mass and 4.6 mM sodium azide were found to be optimal. Under these conditions theoretical yields of ethanol were obtained from 42 g/l xylose within 24 hours.In a fed-batch culture, 62 g/l ethanol was produced from 127 g/l xylose with a yield of 0.49 and a productivity of 1.35 g/l·h.     

Flower formation in excised tobacco stem segments; I. Methodology and effects of plant hormones

The formation of flowers has been studied in stem tissue excised from flowering plants of Nicotiana tabacum variety Wisconsin No. 38, and cultured in vitro on Murashige and Skoog nutrient medium. A procedure for quantitative evaluation of factors influencing floral expression has been developed and effects of the growth substances, indole-3-acetic acid (IAA), kinetin and gibberellic acid (GA₃), on the process are reported.     

Flower Formation in Excised Tobacco Stem Segments; II. Reversible Removal of IAA Inhibition by RNA Base Analogues

The RNA base analogues, 2-thiouracil, 6-azauracil and 8-azaguanine incorporated singly into the medium, increased the number of floral buds in excised stem segments of Nicotiana tabacum variety Wisconsin No. 38 cultured in vitro. Combined treatments with 2 and 3 base analogues were even more effective. The effects were prevented by the corresponding natural counterparts, uracil, uridine, and guanosine respectively. These nucleic acid constituents added to cultures without base analogues did not affect the number of floral buds formed. In stem segments from the lower internodes treatments with the analogues effected a transition from vegetative to floral bud formation, thus in a sense removing the floral gradient as defined by Chouard and Aghion.