Proteins, elementary composition

Knowledge of the amino acids developed slowly during the 19th century, since Mulder (200) and other pioneer workers devoted most of their efforts to the solution of other problems, particularly the elementary composition of proteins. As recently as 1890, Osborne (211) determined the elementary composition of oat-kernel proteins in the first of his now-classical investigations on vegetable proteins. 

To get from the amino acid analysis of the protein to its structure, its molecular weight had to be estimated. As early as 1885 Zinoffsky had reported a minimum molecular weight for hemoglobin of 16.73 kDa based on its elementary composition and assuming one atom of iron/ mole, a remarkably accurate figure. For most proteins because of their large size and ease of denaturation, classical cryoscopic or ebulliscopic methods were impracticable. Osmotic pressure measurements were... 

Except the protamines, the histones and the derivatives of the proteins, all the proteins contain carbon, hydrogen, nitrogen, sulphur and oxygen, and they possess the following elementary composition —... 

Adair and Robinson (1) indicate that the refractive index of a protein or an amino acid is approximately determined by its elementary composition however, the structure of a molecule is also of importance. The values reported for amino acids are scattered and fragmentary (1, 10), and prior to our preliminary communication (25) no systematic investigation had accounted quantitatively for the relationship... 

Because the amino group is on the a-carbon, the amino acids with this general formula are known as a-amino acids. The a-carbon atom becomes asymmetric when R is not an H atom. Naturally occurring amino acids have an L-configuration. Amino acids are the building blocks of proteins, and the elementary composition of most proteins is similar the approximate percentages are ... 

Table 30.4 gives the structure of R, molecular weight, and elementary composition of each of the 20 amino acids commonly found in proteins. 

While it cannot be denied that the soundest methods for the estimation of pure albumin in aqueous solution are likely to be those based on elementary composition (i.e., carbon or nitrogen) or measurement of peptide bonds (e.g., far-ultraviolet spectrophotometry) the oft-repeated statement that the Kjeldahl nitrogen method for determining plasma proteins is theoretically more sound than others is untrue. This method suffers no less than others from the disadvantage that the individual plasma proteins possess different nitrogen contents (Table 3). 

From almond emulsin, enzymes with a jS-glucosidase value as high as 16 have been prepared. (The ordinary almond emulsins have a value of 1 or less.) The properties of such preparations have been studied by Helferich and associates (16). The elementary composition agrees with that of protein substances, but the hydrogen content is somewhat greater than usual. The protein nature of the material also agrees with the action of the anions of neutral salts on the enzymic activity since the order of activation by... 

Protein, prepared by the second method, specifically that of Arthur and others (7,10), has an elementary composition on a moisture-free basis as follows 16.23% of nitrogen (Kjeldahl), 0.74% of ash, and 0.06% of fat. 

Data on the elementary composition of hemocyanins from many species are reported in Table V. According to their copper content hemocyanins are divided in two groups those of molluscs in which it amounts to 0.24-0.26% of the dry weight and those of arthropods in which it accounts for only 0.17-0.18%. Discrepancies in the values reported by earlier authors must be attributed either to impurities present or to the method of determination. The hemocyanins do not contain any heavy metal other than copper (Gatterer and Philippi, 1933). Hernler and Philippi (1933) measured 11.5% water in crystalline hemocyanin, a relatively low value compared with other proteins. The sulfur content is also fairly low, 0.7-1.2% in all hemocyanins examined, and appears to have no relation with the copper content. In hemocyanin from Umultts poliphemus the sulfur derives half from cystine and half from methionine (Mazur, 1937). 

The assembly-disassembly cycle of CO PI and COPII coats is controlled by the GTPase cycle of the small G proteins Arfl and Sar. We describe here two spectroscopic assays that enable real-time studies of some elementary steps of coat assembly and disassembly on artificial liposomes of defined composition and curvature. A flotation assay to assess the effect of membrane curvature on protein adsorption to liposomes is also presented. 

---