OCTOBEB 2, 1908] 



SCIENCE 



425 



proteins, and there is no indication that 

 any essential difference exists in the gen- 

 eral character of the structure of the pro- 

 teins from these two forms of life. Some 

 of the seed proteins, like some of those 

 from animals, lack one or more of the 

 amino-acids; and zein, from maize, lacks 

 glycocoll, tryptophane and lysine. The 

 crystalline glubolins, which are possibly 

 more definite chemical individuals, have 

 yielded on hydrolysis as complicated a 

 mixture of amino-acids as any of the 

 amorphous preparations. These, therefore, 

 furnish no ground for the assumption that 

 the several proteins, as we now know them, 

 are mixtures of less complex substances. 



Of twenty-three different seed proteins 

 which have been hydrolyzed, all have 

 yielded leucine, proline, phenylalanine, 

 aspartic acid, glutaminic acid, tyrosine, 

 histidine, arginine and ammonia. Five 

 have yielded no glycocoll. Two yielded no 

 alanine which could be positively identi- 

 fied, but did yield impure products which 

 left little doubt but that this amino-acid 

 was present. Four yielded no lysine, and 

 one, no tryptophane. Four of these pro- 

 teins yielded extremely small quantities of 

 cystine, three others, none. The remain- 

 ing sixteen have not yet been examined for 

 this amino-acid on account of the difficul- 

 ties encountered in separating small quan- 

 tities of it. No attempt has yet been made 

 to isolate isoleucine. If this amino-acid is 

 yielded by the seed proteins it will prob- 

 ably be found in the mixture of undeter- 

 mined substances from the third fraction 

 of the esters, which has not been converted 

 into products suitable to weigh. Glyco- 

 coll, lysine and tryptophane are the only 

 amino acids that have been proved lacking 

 in any one of these proteins. 



In respect to the quantitative relations 

 of the amino-acids, the fact must not be 

 overlooked that the determinations of many 

 of them are to be regarded only as ap- 



proximations to the amounts actually 

 yielded by the protein. The determina- 

 tions of the monamino-acids by Fischer's 

 method are doubtless comparable within 

 certain limits, if sufficient care is exercised 

 in conducting the analysis. The quanti- 

 ties of these amino-acids recovered are un- 

 questionably less than those actually pres- 

 ent, for esterification is never complete and 

 the losses incident to the separations by 

 fractional crystallization are not incon- 

 siderable. Under uniform conditions, 

 however, losses are nearly uniform and the 

 figures representing the quantities of 

 amino-acids found give a good idea of dif- 

 ferences and similarities between the dif- 

 ferent proteins. Such figures are in most 

 cases comparable to within perhaps one per 

 cent, of the protein, and probably repre- 

 sent about seventy-five per cent, of the total 

 quantity of the amino-acids which are de- 

 termined that were originally formed by 

 hydrolysis, providing that these amino- 

 acids are first subjected to two well-con- 

 ducted esterifications. Most uncertainty 

 attaches to the results obtained for valine 

 and serine, which are separated from as- 

 sociated substances with such difficulty 

 that the determinations of them must be 

 regarded as simply qualitative. Alanine 

 also is difficult to separate in a condition 

 fit for weighing, and no importance is to 

 be attached to differences in the amount of 

 this amino-acid unless these are pro- 

 nounced. 



A very extensive experience, however, 

 with determinations, of arginine, histi- 

 dine and lysine has convinced me that it 

 is possible to make quantitative determina- 

 tions of these bases which are very accu- 

 rate. The results of these determinations 

 can be controlled by comparing the amount 

 of nitrogen contained in the quantities 

 found with that precipitated by phospho- 

 tungstic acid under definite conditions 

 which have been worked out in my labora- 



