Kalata B1 is a member of a new family of polypeptides, isolated from plants, which have a cystine knot structure embedded within an amide-cyclized backbone. This family of molecules are the largest known cyclic peptides, and thus, the mechanism of synthesis and folding is of great interest. To provide information about both these phenomena, we have synthesized kalata B1 using two distinct strategies. In the first, oxidation of the cysteine residues of a linear precursor peptide to form the correct disulfide bonds results in folding of the three-dimensional structure and preorganization of the termini in close proximity for subsequent cyclization. The second approach involved cyclization prior to oxidation. In the first method, the correctly folded peptide was produced only in the presence of partially hydrophobic solvent conditions. These conditions are presumably required to stabilize the surface-exposed hydrophobic residues. However, in the synthesis involving cyclization prior to oxidation, the cyclic reduced peptide folded to a significant degree in the absence of hydrophobic solvents and even more efficiently in the presence of hydrophobic solvents. Cyclization clearly has a major effect on the folding pathway and facilitates formation of the correctly disulfide-bonded form in aqueous solution. In addition to facilitating folding to a compact stable structure, cyclization has an important effect on biological activity as assessed by hemolytic activity.

No abstract

Polyphenol oxidase (PPO) activity of Russet Burbank potato was inhibited by sense and antisense PPO RNAs expressed from a tomato PPO cDNA under the control of the 35S promoter from the cauliflower mosaic virus. Transgenic Russet Burbank potato plants from 37 different lines were grown in the field. PPO activity and the level of enzymatic browning were measured in the tubers harvested from the field. Of the tubers from 28 transgenic lines that were sampled, tubers from 5 lines exhibited reduced browning. The level of PPO activity correlated with the reduction in enzymatic browning in these lines. These results indicate that expression of tomato PPO RNA in sense or antisense orientation inhibits PPO activity and enzymatic browning in the major commercial potato cultivar. Expression of tomato PPO RNA in sense orientation led to the greatest decrease in PPO activity and enzymatic browning, possibly due to cosuppression. These results suggest that expression of closely related heterologous genes can be used to prevent enzymatic browning in a wide variety of food crops without the application of various food additives.

No abstract

No abstract

The ability to minimize potato yield and quality losses due to drought can be greatly improved by understanding the relative responses of different cultivars to seasonal variations in water supply. To address this need, we initiated a 2 year field experiment to determine the responses of the six potato cultivars to different seasonal drought patterns, including 1) full season irrigation at 100 % ET, 2) irrigation at 100 % ET terminated during late bulking , 3) full season irrigation at 70 % ET , 4) irrigation at 70 % ET terminated during late bulking , and 5) a gradual reduction in irrigation from 100 % ET during tuber initiation through early bulking, to 70 % ET during mid-bulking, and 50 % ET through late bulking. GemStar Russet and Ranger Russet, two medium-late maturing cultivars, generally produced the highest yields across the range of drought treatments, but both were fairly sensitive to changes in drought severity. Alturas, a late maturing cultivar, produced relatively high yields with full irrigation, but exhibited the greatest sensitivity to increasing drought severity, particularly when severe late-season water deficits were imposed. Yields for the early maturing cultivar Russet Norkotah were relatively low overall, but it was the least sensitive to changes in drought severity, particularly when late season drought was imposed. Russet Burbank produced comparatively high total yields across the range of drought treatments, but U.S. No. 1 yields were substantially reduced by each seasonal drought pattern. However, it was less sensitive to changes in drought severity than GemStar Russet, Ranger Russet and Alturas. Total and U.S. No. 1 yields for Summit Russet were low for each drought treatment and it exhibited intermediate sensitivity to changes in drought severity. GemStar Russet had the highest water use efficiency based on U.S. No. 1 yield.Resumen Se puede mejorar grandemente la habilidad para minimizar las pérdidas en rendimiento y calidad de papas debido a la sequía, mediante el entendimiento de las respuestas relativas de diferentes variedades a variaciones estacionales en el suministro de agua. Para atender esta necesidad, iniciamos un experimento de campo por dos años para determinar las respuestas de seis variedades de papa a diferentes patrones de sequía estacional, incluyendo, 1) riego completo en el ciclo al 100 % ET, 2) riego al 100 % ET terminando durante el fin de la tuberización, 3) riego durante todo el ciclo a 70 % ET, 4) riego al 70 % ET terminando al final de la tuberización, y 5) reducción gradual de riego de 100 % ET durante la iniciación de la tuberización a lo largo del llenado temprano, a 70 % ET durante la mitad del llenado, y 50 % ET a lo largo de la tuberización tardía. Gem Star Russet y Ranger Russet, dos variedades de intermedias a tardías, generalmente produjeron los rendimientos más altos a lo largo de la amplitud de los tratamientos de sequía, pero ambas fueron muy sensibles a los cambios de la severidad de la sequía. Alturas, una variedad tardía, produjo rendim...

A series of reduced-size hexapeptide analogues of LH-RH were synthesized that contain the residues corresponding to amino acid positions 4-9 and are linked to various carboxylic acids in place of residue 3. These compounds were tested in vitro in the rat pituitary receptor binding and LH release assays. A wide range of binding affinities was obtained up to and exceeding that of LH-RH. Both agonists and antagonists were obtained. From the SAR studies, it appears that a very precise size, length, and shape of the substituent at position 3 is required to achieve agonist activity, whereas the structural requirements for antagonist activity appear to be much less stringent. Depending on the nature of the substituent at positions 6 and 4, the biological response switches from antagonist to agonist or vice versa. The results suggest that conformational changes at position 6 or 4 feed back to the substituent at position 3, which induces the change from agonist to antagonist. The most potent compounds in the series were tested in vivo and found to be active.

~~~Factors affecting the production of amidocarboxy-substituted free radicals have been investigated by examining reactions of derivatives of valine and sarcosine. Variations in the regioselectivity of reactions of these compounds are exemplified by the reactions of N-benzoylvaline methyl ester (4a) and Nbenzoylsarcosine methyl ester (1 2a) with sulphuryl chloride and N-bromosuccinimide. Whereas the reaction of (4a) with sulphuryl chloride involves hydrogen-atom transfer from the P-position of (4a) with subsequent chlorine incorporation to give (4g), in direct contrast the reaction with Nbromosuccinimide proceeds via hydrogen-atom abstraction from the a-position of (4a) and yields the dibromide (4). N-Benroylsarcosine methyl ester (1 2a) reacts with N-bromosuccinimide t o give the a-bromosarcosine derivative (1 Zb), whereas with sulphuryl chloride the product is the N-chloromethylglycine derivative (1 2c). These studies indicate that amidocarboxy-substituted radicals such as (3a) and (13) are considerably more stable than the tertiary alkyl radical (la) and the amidosubstituted radical (14), respectively, but hydrogen-atom transfer reactions may afford the less stable products if electrophilic radicals are involved in the hydrogen-atom abstraction and if there is little development of radical character in the reaction transition state.