pH dependence of the urea and guanidine hydrochloride denaturation of ribonuclease A and ribonuclease T1

To investigate the pH dependence of the conformational stability of ribonucleases A and T1, urea and guanidine hydrochloride denaturation curves have been determined over the pH range 2-10. The maximum conformational stability of both proteins is about 9 kcal/mol and occurs near pH 4.5 for ribonuclease T1 and between pH 7 and 9 for ribonuclease A. The pH dependence suggests that electrostatic interactions among the charged groups make a relatively small contribution to the conformational stability of these proteins. The dependence of delta G on urea concentration increases from about 1200 cal mol-1 M-1 at high pH to about 2400 cal mol-1 M-1 at low pH for ribonuclease A. This suggests that the unfolded conformations of RNase A become more accessible to urea as the net charge on the molecule increases. For RNase T1, the dependence of delta G on urea concentration is minimal near pH 6 and increases at both higher and lower pH. An analysis of information of this type for several proteins in terms of a model developed by Tanford [Tanford, C. (1964) J. Am. Chem. Soc. 86, 2050-2059] suggests that the unfolded states of proteins in urea and GdnHCl solutions may differ significantly in the extent of their interaction with denaturants. Thus, the conformations assumed by unfolded proteins may depend to at least some extent on the amino acid sequence of the protein.     

Intestinal microsomes: polyunsaturated fatty acid metabolism and regulation of enterocyte transport properties

Recent evidence has suggested that transport of nutrients from the lumen to the interior of the gastrointestinal epithelium and exit of nutrients from the enterocyte to the circulation is governed by physicochemical properties of brush border and basolateral membranes, respectively. The main determinants of membrane properties are phospholipid, cholesterol, and fatty acyl chain composition (chain length and degree of unsaturation). Lipid synthesis occurs in enterocyte microsomes and the fine tuning of lipid composition is done at other subcellular sites by deacylation-reacylation or by changing the polar head group (e.g., by phosphatidylethanolamine methyltransferase). The present paper will focus on the mechanisms by which enterocyte membranes adapt functional properties in response to external stimuli. It is proposed that under the influence of internal or external stress, the enzymes of lipid metabolism in microsomes are modulated. These changes in lipid synthesis are reflected in other subcellular membranes, changing their physicochemical status and thus transport phenomena. One of the initial events appears to be alteration in desaturase enzyme activity. Our results suggest that desaturase activity and the fatty acyl profiles of the intestinal mucosal phospholipid rapidly respond to physiological conditions such as fasting and dietary fat treatment.     

Acetyl coenzyme a carboxylase activity in developing seedlings and chloroplasts of barley and its virescens mutant

Acetyl coenzyme A (CoA) carboxylase activity of whole tissue homogenates and chloroplast preparations was analyzed as the acetyl-CoA-dependent incorporation of [¹⁴C]bicarbonate into an acid-stable product. The absolute requirement for ATP and MgCl₂, the complete inhibition with avidin, and end-product analysis were consistent with the presence of acetyl-CoA carboxylase activity. Little difference was found between the mutant and normal tissue homogenates from the 1- to 3-day growth stages, during which period both showed a 3-fold increase. However, by 4 days, the activity of the mutant exceeded that of the normal. Fractionation studies showed that the enzyme was a soluble protein present in the stromal fraction of chloroplasts. The biotin content was also highest in the stroma, although it was found in the lamellar fraction as well. For both the mutant and the normal, the highest acetyl-CoA carboxylase activities were obtained in the stromal preparations from 4-day seedlings (54 and 31 nmoles per milligram protein per minute for the mutant and the normal, respectively) with a progressive decline by 6 and 8 days. The difference between the mutant and the normal was not due to the accumulation of an inhibitor in the normal.     

Pollen carryover,nectar rewards,and pollinator behavior with special reference to Diervilla lonicera

Summary Pollen carryover was measured in three species of bumble bee pollinated plants by counting the numbers of foreign grains applied to the stigmas of a series of flowers by bumble bees. Deposition declined with the number of flowers visited in a roughly exponential fashion; most grains were deposited on the first few flowers, but some grains went much farther, the maximum carryover being 54 flowers. Variation in deposition was very high. In Diervilla lonicera, bees desposited significantly more grains on flowers which contained large amounts of nectar than on drained flowers. The implications are discussed in terms of plant strategies for optimizing pollination.     

Mutagenic activity of Fusarium moniliforme isolates in the Salmonella typhimurium assay.

A total of 33 isolates of Fusarium moniliforme from several food or feed crops were grown on sterile cracked corn, and chloroform-isopropanol extracts were assayed for mutagenic activity in the Salmonella typhimurium-microsome system by using tester strain TA98 or TA100 or both. Extracts of 21 (64%) of the isolates assayed against TA100 were mutagenic. Activities of seven of these extracts were increased markedly with incorporation of the liver homogenate (S-9) into the assay. Seven (33%) of the isolates assayed against TA98 were weakly active, with the liver homogenate having little effect on reversion rates.     

Flunisolide nasal spray for perennial rhinitis in children.

Twenty-seven children with perennial rhinitis entered a double-blind cross-over study comparing nasal sprays of flunisolide---a new topical corticosteroid---and placebo. Symptoms were assessed over two consecutive monthly periods with each treatment. Weekly diary cards, monthly clinical assessments, and end-of-trial preferences all favoured the active drug. At the end of the trial 20 patients preferred the treatment month with flunisolide, four preferred the placebo month, and two rated the periods equally. Side effects were mild, the commonest being transient nasal stinging. Seventeen children who derived benefit from flunisolide continued with the treatment for a six-month open-study period. Many reduced the dosage from three times to twice or once daily without losing benefit. The effect of flunisolide on the pituitary-adrenal axis was assessed in seven children by measuring the 0900 blood cortisol concentrations at two-month intervals over the six months. No effect was observed. The results show that flunisolide is effective and safe for the treatment and prophylaxis of perennial rhinitis in children.     

Study of Candida ingens grown on the supernatant derived from the anaerobic fermentation of monogastric animal wastes.

A pellicle-forming yeast, identified as Candida ingens, was found to grow on substrates derived from the anerobic fermentation of monogastric animal wastes. The organism used volatile fatty acids C2 to C6 and ammonia nitrogen. It had a preferential uptake of the acids in increasing order of molecular weight, removing 90% of the total titratable volatile acid. The nonwrinkled pellicle had a doubling time of 3.2 h, and the doubling time of the wrinkled pellicle was 4.2 h. Proximate amino acid and nucleic acid analyses suggested that the organism might be acceptable as a source of single cell protein. Its vitamin B group content compared favorably with that of other yeasts. It contained 6% calcium and 7% phosphorus. It could be useful in removing these minerals from effluents as well as in providing them as nutrients in livestock rations.     

An ultrastructural study of two forms of chilling-induced injury to the rind of grapefruit (Citrus paradisi, Macfed).

The ultrastructural manifestations of storage chilling-injury and concentric ring stipple indicate that the two types of injury are similar in some respects and different in others.The low temperature storage-induced injury involves the epidermal cells and several layers of epicarpal cells below. It is manifested as an increase in lipid material in the cytoplasm and vacuole and in eventual degradation and collapse of the cytoplasm. The field injury, concentric ring stipple, apparently involves primarily the epidermal cells which become extremely electron dense. The epicarp cells of the injured region do not show extensive damage but do exhibit increased lipid accumulation. This accumulation of lipid is a phenomenon common to both types of injury and may be indicative of an altered metabolism due to the low temperatures. The apparent loss of organization and compartmentation in the chilling injury is also suggestive of membrane degradation.The storage chilling-injury occurs after exposure to low temperatures for several weeks, whereas the concentric ring stipple is evidently induced by an exposure in the field for only a few hours. The ultrastructural differences observed in these two injuries, therefore, may be due to the different time- and stress- factors involved.