Strategy and tactics in protein chemistry

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An assessment of methanolysis and other factors used in the analysis of carbohydrate-containing materials

The stability of monosaccharides in methanolic hydrochloric acid of different strengths and at different temperatures was determined. They are generally stable for 24h in methanolic 1m- and 2m-hydrochloric acid at both 85 degrees C and 100 degrees C, but undergo considerable destruction in methanolic 4m- and 6m-hydrochloric acid at 100 degrees C. Analysis of glycopeptides and oligosaccharides of known composition showed that release of carbohydrate was complete within 3h in methanolic 1m-hydrochloric acid at 85 degrees C. Removal of methanolic hydrochloric acid by rotary evaporation resulted in considerable losses of monosaccharides, which could be prevented by prior neutralization. Methanolysis caused extensive de-N-acetylation of acetamidohexoses, so that a re-N-acetylation step is necessary in the analytical procedure. The addition of acetic anhydride for this purpose also prevented loss of internal standard by adsorption on the insoluble silver salts used in neutralization. Several trimethylsilylating agents were studied and suitable conditions are recommended. The effects on the analytical system of water and some common organic and inorganic contaminants are assessed.

The use of maleic anhydride for the reversible blocking of amino groups in polypeptide chains

1. Maleic anhydride was shown to react rapidly and specifically with amino groups of proteins and peptides. Complete substitution of chymotrypsinogen was achieved under mild conditions and the extent of reaction could be readily determined from the spectrum of the maleyl-protein. 2. Maleyl-proteins are generally soluble and disaggregated at neutral pH. Trypsin splits the blocked proteins only at arginine residues and there is frequently selectivity in this cleavage, e.g. in yeast alcohol dehydrogenase and pig glyceraldehyde 3-phosphate dehydrogenase. 3. The group is removed by intramolecular catalysis at acid pH. The half-time was 11-12hr. at 37 degrees at pH3.5 in in-maleyl-lysine or in maleyl-chymotrypsinogen. 4. The unblocking reaction can be used as the basis for a ;diagonal'-electrophoretic separation of lysine peptides and N-terminal peptides, as shown by studies with beta-melanocyte-stimulating hormone.

A MoS2 /PTCDA Hybrid Heterojunction Synapse with Efficient Photoelectric Dual Modulation and Versatility

Just as biological synapses provide basic functions for the nervous system, artificial synaptic devices serve as the fundamental building blocks of neuromorphic networks; thus, developing novel artificial synapses is essential for neuromorphic computing. By exploiting the band alignment between 2D inorganic and organic semiconductors, the first multi-functional synaptic transistor based on a molybdenum disulfide (MoS₂ )/perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) hybrid heterojunction, with remarkable short-term plasticity (STP) and long-term plasticity (LTP), is reported. Owing to the elaborate design of the energy band structure, both robust electrical and optical modulation are achieved through carriers transfer at the interface of the heterostructure, which is still a challenging task to this day. In electrical modulation, synaptic inhibition and excitation can be achieved simultaneously in the same device by gate voltage tuning. Notably, a minimum inhibition of 3% and maximum facilitation of 500% can be obtained by increasing the electrical number, and the response to different frequency signals indicates a dynamic filtering characteristic. It exhibits flexible tunability of both STP and LTP and synaptic weight changes of up to 60, far superior to previous work in optical modulation. The fully 2D MoS₂ /PTCDA hybrid heterojunction artificial synapse opens up a whole new path for the urgent need for neuromorphic computation devices.

The preparation of DTPA-coupled antibodies radiolabeled with metallic radionuclides: an improved method

Isotopes of iodine are often employed as radiolabels for antibodies used in radioimmunodetection studies in which tumor localization is determined by external imaging. Because of drawbacks associated with the use of these isotopes, alternative labeling methods have been considered; such as covalently attaching strong chelators so that the coupled protein may be radiolabeled with metallic radionuclides by chelation. We have developed a method of coupling the strong chelator diethylenetriaminepentaacetic acid (DTPA) which is simple, efficient, and superior to reported methods. Using the cyclic anhydride, coupling to IgG antibody is about 75% efficient and is completed in less than 1 min at neutral pH. Because the concentration of hydrolytic products is small, the coupled protein is rapidly purified for use or storage. Labeling of the protein is also accomplished rapidly and the labeled product has been shown to be stable both in vitro and in vivo.

Measurement of Urinary d- and l-2-Hydroxyglutarate Enantiomers by Stable-Isotope-Dilution Liquid Chromatography–Tandem Mass Spectrometry after Derivatization with Diacetyl-l-Tartaric Anhydride

Background: The differential diagnosis of d-2-hydroxyglutaric aciduria (d-2-HGA), l-2-hydroxyglutaric aciduria (l-2-HGA), and the combined d/l-2-hydroxyglutaric aciduria (d/l-2-HGA) can be accomplished only by the measurement of the corresponding 2-hydroxyglutarate (2-HG). Available methods for the determination of d- and l-2-HG in urine are either time-consuming and expensive or have not been extensively validated. We aimed to develop a method for their rapid and sensitive measurement.

Methods: We used liquid chromatography–tandem mass spectrometry (LC-MS/MS) for the determination of d- and l-2-HG with stable-isotope-labeled internal standards. Urine samples of 20 μL were mixed with 250 μL of methanol containing the internal standards and subsequently dried under nitrogen. The analytes were derivatized by use of diacetyl-l-tartaric anhydride (DATAN) to obtain diastereomers, which were separated on an achiral C18 HPLC column and detected by MS/MS in multiple-reaction-monitoring mode.

Results: The use of DATAN as chiral derivatization reagent provided very well separated peaks of the formed diastereomers of d- and l-2-HG, with a total runtime of 5 min. The inter- and intraassay CVs for d- and l-2-HG ranged from 3.4% to 6.2%. Mean recoveries of d- and l-2-HG, evaluated on two concentrations, were 94%. Detection limit of the presented method was 20 pmol for a sample volume of 20 μL. Method comparison of the LC-MS/MS method with a gas chromatography–mass spectrometry method, in which d- and l-2-HG were derivatized with R-(−)-butanol, showed good agreement between the two methods.

Conclusions: Urinary d- and l-2-HG can be analyzed by MS/MS after derivatization with DATAN. The presented method may be suitable for the differential diagnosis of 2-HGA.

Competitive labelling, a method for determining the reactivity of individual groups in proteins. The amino groups of porcine elastase

1. A method is described for determining the ionization constants and reactivities of individual amino groups in proteins. The principle is that in the presence of a trace amount of radioactive label, the various reactive groups in a protein molecule will compete for the label and the amount incorporated into any one group will be determined by its nucleophilicity, pK and micro-environment. The relative amounts of label incorporated into various groups will be proportional to their second-order rate constants and by comparing these rate constants with those expected on the basis of a linear free-energy relationship obtained with a series of standard compounds, the micro-environment can be defined for a particular amino group. 2. The method consists of treating a protein and an internal standard with a limiting amount of radioactive reagent and then with an excess of unlabelled reagent to yield a chemically homogeneous but heterogeneously labelled compound. After appropriate enzymic digestion peptides containing each labelled group are isolated and their rates of reaction, relative to the internal standard, are determined from their specific radioactivities. The entire procedure is repeated at several pH values. 3. When the method was applied to the amino groups of porcine elastase by using tritiated acetic anhydride as the labelling reagent, the N-terminus was found to have pK(a) 9.7 and a much lower than normal reactivity. Lysine-87 and lysine-224 were found to have pK(a) 10.3 and normal reactivities. At pH values greater than 10.5 there are discontinuities in all the titration curves, indicating that the entire molecule is undergoing a structural reorganization.