Conformational properties of the N-terminal residues of S-peptide. I. The ribonuclease S′ system

The contribution of the 1–6 N-terminal sequence to the conformational properties of the S-peptide (the 1–20 sequence of ribonuclease A) was assessed by determining in the ribonuclease S′ system the helical content and the binding capability of synthetic [Orn¹⁰]-S-peptide analogs, in which lysine¹, glutamic² and threonine³ were progressively deleted, alanine⁴ and alanine⁵were alternatively replaced by serine, and alanine⁶ was substituted by serine or proline. Both the deletion of the three N-terminal residues and the alanine⁶/proline replacement produces the loss of the helical structure up to lysine⁷. No or minor effects are found in all other cases. From the comparison of the binding data, the energy for the conformational stabilization of the N-terminal region was calculated to amount to 1.4 kcal/mol. The results are discussed in comparison with the known x-ray data of the enzyme, with some predictive rules of secondary structure which were applied to this region and with the known phylogenetic variance of the residues in this region.     

The influence of amino acid side-chains on α-helix stability: S-peptide analogues and related ribonucleases S′

In order to determine the influence of amino acid side-chains on α-helix stability, in relation to the protein folding process, the coil-helix transitions of some synthetic [Orn 10]-S-peptide analogues, containing, in position 8, Phe, Tyr, Ile, Ala, cpGly² and Gly, were investigated by the technique of circular dichroism under two different sets of conditions. First, the transitions of the Speptide analogues in water/trifluoroethanol mixtures were recorded. From the pattern of the transitions and from the ellipticity values in 97% trifluoroethanol, the following increasing order of amino acids as α-helix formers was found: Gly < Tyr ≤ Phe < cpGly < Ala < Ile. This finding indicates that the conformational parameters (Chou & Fasman, 1974) of the residues in position 8 play an important but not exclusive role in α-helix stability, since the hydrophobicity of the side-chain (Nozaki & Tanford, 1971) of residue 8 exerts a strong influence. From the second approach, studying the capability of the S-peptide analogues to bind to S-protein, the following increasing order was found: (Gly, Ala) < Ile < cpGly < Tyr < Phe. This result reveals that the conformational parameters of the residues in position 8 play no role, whereas their hydrophobic character and side-chain interactions with surrounding residues in the S-protein portion are the determining binding factors. This finding explains the reason for the Phe8 invariance in RNAase A during evolution, and furnishes evidence for the relevant role of long-range interactions in the protein folding process.     

Studies on cytochrome c. XI. Circular dichroism studies on synthetic peptides related to the C-terminal region of baker's yeast iso-1-cytochrome c

Circular dichroism studies on synthetic peptides related to the C-terminal region of yeast iso-1-cytochrome c were carried out and compared with conformational studies on horse cytochrome c fragments. Evidence is presented for a weaker predisposition for ordered structure in the former peptides when compared with the corresponding region in horse cytochrome c. These findings agree with theoretical predictions and with observations that yeast and other mammalian type cytochromes c differ in several minor respects.     

Energy transduction in photosynthetic bacteria. VIII. Activation of the energy-transducing ATPase by inorganic phosphate

ATPase activity and ATP-induced energization of photosynthetic membranes from Rhodopseudomonas capsulata are stimulated by phosphate; the maximum stimulatory effect occurs at a concentration between 1 and 2 mM.The sensitivity of the ATPase to oligomycin increases in the presence of phosphate since all the P_i-stimulated activity is inhibited by this antibiotic. Aurovertin, which has no effect on ATPase in the absence of phosphate, inhibits completely the activity elicited by this anion.The addition of P_i induces a substantial increase in the V of ATPase activity without changing the affinity of the enzyme for ATP or ADP.Arsenate, at the same concentrations, produces effects very similar to those of phosphate. The stimulation by arsenate of the transfer of energy from ATP to the membrane suggests a non-hydrolytic role of this anion as a modifier of the ATPase activity.     

Plasmolyse und Permeabilität

Ohne Zusammenfassung Mit 3 Textfiguren     

An improved breeding method for solitarious locusts

In order to unravel the physiological, endocrine, and behavioral differences between gregarious and solitarious forms of the desert locust, Schistocerca gregaria (Forsk.) (Orthoptera, Acrididae), a constant supply of rather large numbers of solitary individuals has to be guaranteed. This represents a bottleneck, mainly because of the intensity of the labor involved and limited laboratory accommodation. The method we describe here substantially reduces the space and manpower needed. The survival rate we obtained in the solitarised population was relatively high, reaching about 55%. The optimal rearing temperature proved to be 32–36 °C. Cabbage leaves and oat flakes sufficed for feeding all year round. Special racks have been designed that enable high density stacking and easy handling. The solitarisation process was monitored over ten consecutive generations. Changes in morphometrics, eye stripes, color, and behavior were recorded, of which only morphometrics, temperature related development, and mortality are discussed. A shift towards the solitarious phase was recorded, with clear differences between gregarious, 1^st generation and 7^th to 10^th generation solitarious locusts.