Page:EB1922 - Volume 30.djvu/689

Rh

xxx:o^

Flavone

,-r

sA

by hydrolysis, into the two simple compounds, salicylic acid and acetophenone, from which it may well be formed in the plant:

f^v-XJ-CCsHs

Cft +2M!U=| |_ + ,

CHj

Aceto- phenone

The plant yellows are hydroxy-derivatives of flavone, varying in the manner and position of the hydroxyl groups; but whilst some are flavones in which these groups are contained only in the benzene sections of the molecule, others are.flavenols, i.e. deriv- atives of the simple hydroxy-compound

+2H!0

J CO.OH Salicylic acid

The plant colouring matters other than the yellows which are now generally grouped as anthocyan colours, are derived from the yellows by a very simple process merely by reduction, a process, however, which involves their conversion into deriva- tives of ortho-quinone, as shown by the following equation repre- senting the change of the flavonolquaratin into cyanin chloride:

Cl

, (OH),


 * OH

OH

The colour produced by an anthocyan depends not only on the number and position of the hydroxyl groups but also on its con- dition, in the plant cell whether it be present in combination with acid or as a salt.

Nuclear Materials. Substances which play a determining part as structural elements, if not as functional agents, are far more complex. The nucleic acids are the chief. Nucleic acid, from yeast or the wheat embryo, for example, which has the formula CsgH^OsNisC,,, may be resolved into four sections known as nucleotides, all of which have been isolated and studied of late years, particularly by the American chemists, Levene and others. Each of these nucleotides consists of the peculiar pentose, ribose, associated, on the one hand, with phosphoric acid, on the other, with a purine base (a compound of the uric acid series), the two former being common to all four sections but each having its special basic constituent, namely, one of the following: N = C.NH 2 HN CO ' N=C.NH, HN CO

II II II II

HCC NH HN:C C NH OC CH OC CH

\ \

II II CH I II CH | II I II

N C N HN C N HN CH HN CH

Adenine Guanine Cytosine Uracil

Nucleic acid of animal origin contains a hexose in place of the pentose, ribose; moreover, the basic elements are not all the same, jnethyluracil (thymine) taking the place of uracil. The formula assigned to plant nucleic acid is: HO \ OP.O.C 5 H,O 2. C 6 H 4 N S O


 * I Guanine unit

HO O HO \

HO

OP.O.CsHsO. C 4 H 4 N 3 O


 * Cytosine unit

HO O

\

OP.O.C S H 6 O. C 6 H 4 N 6 I I Adenine unit

HO O HO \

OP.O.C 6 H 7 O 2. C 4 H 3 N 2 Oj
 * Uracil unit

HO

Phosphoric Ribose. unit unit

Complex materials thus constituted, comprising acid, neutral and basic sections, this last of varying structure, obviously must offer numerous attractions such as befit a nuclear substance; probably, however, the phosphoric units are the main functional elements, and it is in these compounds particularly that the special value of phosphoric acid to the living organism is appar- ent. The nucleins are accompanied by a number of enzymes which, doubtless, are concerned in their formation; these suffice not only to resolve them, when necessary, into their proximate components but also to convert the basic units into uric acid.

The Proteins. The fundamental phenomena of vital activity are best studied, at present, with the aid of carbohydrate ma- terial, because of its greater simplicity; there is, however, every reason to suppose that, in the main, the same considerations ap- ply to the problems offered by nitrogenous materials. The pos- sibilities are more numerous but the lines of action and reaction are of the same order. The contexture and configuration of car- bohydrate material cannot be greatly varied; although, as shown in artificial silk, cellulose has strength and a world might be built of carbohydrate material, it would undoubtedly display great poverty of pattern and less colour. The introduction of nitrogen has added enormously to structural variety and strength. Else- where the complex carbohydrates have been compared with pave- ments of simple mosaic; the proteins, which play so large a part, especially in animal life, are more like a jig-saw puzzle.

The proteins are the formative materials of animal structures. They are commonly known in such materials as wheat glutin easily separated from the accompanying starch by kneading flour in a gently-running stream of water; egg white; milk casein; glue or gelatin; and as the chief constituent of meats. A number of proteins have been obtained in crystalline form, but they are undoubtedly all substances of high molecular weight. Like the higher carbohydrates they can be resolved into simple units by hydrolysis either by acids or by enzymes. They yield a numer- ous and varied series of fragments; the following is a list of com- pounds of the glycine type thus far separated from them:

Glycine CH 2 (NH 2 ).COOH

Alanine CH 3 .CH(NH 2 ).COOH

Valine (CH 3 ) 2 :CH.CH(NH,)COOH

Leucine(CH 3 ) 2 :CH.CH 2 .CH(NH 2 ).COOH

Isoleucine (CH 3 )(C 2 H 6 ) :CH.CH(NH 2 ).COOH

Serine CH 2 OH.CH(NH 2 ).COOH

Lysine H 2 N.CH 2 CH 2 CH 2 CH(NH 2 ).COOH

NHi

/ Arginine HN=C

NH.CH 2 .CH 2 .CH 2 CH(NH 2 ).COOH Phenylalanine C 6 H 5 .CH 2 .CH (NH 2 ).COOH Tyrosine HO.C 6 H4.CH 2 CH(NH2).COOH Aspartic acid HOOC.CH 2 .CH(NH 2 ).COOH Glutamic acid HOOC.CH 2 .CH 2 .CH(NH 2 ).COOH Hydroxyglutamic acid HOOC.CH 2 .CHOH.CH(NH 2 ).COOH Cystine HOOC.CH(NH 2 ).CH 2 S SCH 2 .CH(NH 2 ).COOH Proline CH 2 CH 2

I I

CH 2 CH.COOH \ / NH

Hydroxyproline

HO.CH CH 2

1 1

CH 2 CH.COOH

\ /

NH

Histidine CH

' # \

-N NH

1 |

HC = C CH 2 .CH(NH 2 ).COOH Tryptophane C CH 2 .CH(NH 2 ).COOH

/>\

C 6 H 4 CH \/ NH