Solubility peptides

Poor peptide solubility has been identified as a major obstacle to efficient segment assembly of peptides on a solid phase particularly for fully protected strategies. 1,5,6 Backbone protection directly addresses this problem and is the basis for a general route to the synthesis of small proteins. 7,8 However, the inclusion of backbone protection in a synthesis is not yet automated or routine and requires careful planning. 

An alternative and possibly more simple approach to S-prenylation is based on S-alkylation of suitably protected or unprotected peptides. This method is widely applied particularly when small amounts of S-prenylated peptides are required, whereby preparative RP-HPLC is generally applied for the isolation of the lipopeptides. The S-alkylation methods used are generally those described above. Whilst with suitably protected peptides solubility represents a major problem, which can be bypassed by S-alkylation of the peptide on resin, 61 with unprotected peptides a very efficient tuning of the reaction conditions is required... 

Enzyme activities are based on rates of casein hydrolysis under defined conditions. The products of casein hydrolysis, as defined in this protocol, are those peptides soluble in 5% TCA that can be detected by the bicinchoninic acid (BCA) protein assay (unitbi.i). The amount of TCA-soluble peptide generated during the course of the reaction can actually be quantified by any one of several protein/peptide assays. The color yield in these assays is assumed to be proportional to the amount of peptide in solution. The amount of product/peptide in the reaction mixture is often reported as bovine serum albumin (BSA) equivalents—since standard curves based on this protein may be used to calibrate the assay. Thus, activity units can be expressed as the amount of BSA equivalents generated per unit time. 

Glycosylation of peptides is an efficient method to stabilize peptide by inhibition of enzymatic degradation, to conformationally modify peptide and usually to increase peptide solubility. Peptides glycosylation also creates additional diversity in peptide libraries since the high functionalities and variability of sugar moieties. 

The development of chemoselective reactions to give a native peptide bond at the site of hgation allows the synthesis of proteins with little or no modification to the covalent structure. A native structure at the ligation site is often desirable in the middle of protein structural domains (amino acid 60-120). The challenge of this approach is to form an amide bond chemoselectively in the presence of free amine side chains (Lys) and carboxylate side chains (Glu/Asp). Ideally, no protecting groups should be used for any of the amino acid side chains as they limit peptide solubility and require additional deprotection steps that can severely reduce the yield and convenience of the synthesis. 

Oh-Uchi SK, Yang JY, LeeJS, MurakawaY, and Narita M. Only Weak Dependence of the Protected Peptides Solubility in Organic Solvent on their Amino Acid Sequence. Polym/1996 28 1033-1038. 

Only about 7% of the coagulating enzyme activity is retained in the cheese curd (200) the remaining activity is expelled in the whey. Recently, Dulley (200) observed that cheeses containing normal and double normal amounts of rennet showed very little difference in peptides soluble in dilute trichloroacetic acid after 10 months maturation this suggests that the amount of rennet did not significantly affect proteolytic breakdown of the cheese proteins. Furthermore, Dulley (200) did not observe a significant difference in starch gel electrophoretic patterns of cheese proteins from cheese containing normal and double normal... 

For some electrospray interfaces, the presence of residual TEA in a sample can significantly interfere with ionization, resulting in noisy, potentially uninterpretable spectra. In that case, it is beneficial to redissolve the sample without added TEA and relyophilize prior to analysis. Several cycles of solubilization-lyophilization may be necessary to eliminate interference from TEA. Peptide solubility can occasionally be a problem for ESI-MS. Routinely, the sample is first dissolved in either water or dilute acid... 

Correlation of protected peptide solubility in solution with structure (32, 48,49) ... 

Having determined the structure of the SH-peptide we started investigating the fraction of peptides soluble in 0.1% TFA. The peptides were separated by reversed phase HPLC (Figure 4). Save for one exception all the peptides were obtained in pure state and their sequences were established in a solid-phase protein sequencer in the case of peptides with C-terminal lysine, or in the spinning cup sequenator in the case of peptides C-terminated with arginine (Figure 1,3). 

TCA (trichloro acetic acid) is the reagent classically used to precipitate proteins. It has no effect on smaller peptide solubility. Standard conditions substrate = hemoglobin, T = 25 C, r = 10 min. 

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