Textbook of Biological Chemistry

Front matter

tots avsieieanentt

Wi

Rose ESSN hialeteiete

Preface

In preparing this book it has been my aim to set before the students as briefly and simply as possible the principal facts and theories of biological chemistry. In striving to attain this objective it has manifestly been impossible to include a great amount of material that is of interest and importance to the biochemist. The book is meant first and last for the elementary student and not for reference. I make no pretension of having written an exhaustive account of the subjects which are presented, and I believe that for a book of this sort the ability to omit is fully as important as the ability to include.

I wish to acknowledge my indebtedness to Dr. Aaron Bodansky, whose criticisms have been of great value, to Cleveland Abbe, Jr., Ph.D., and to my wife for the correction of chemist’s English.

Introduction

Definition of Biological Chemistry.—Biological, or physiological chemistry, is the chemistry of living things, or their products. It includes the inorganic, organic, analytical, electro- and physical chemistry of plants and animals. In biological chemistry, chemical combination and chemical reaction, the basis of all chemistry, depend upon the ability of some atoms to lose electrons and of other atoms to take on electrons.

Aims and Ideals of Biological Chemistry.—The aim of the biological chemist is to explain the chemical composition of plants and animals and the chemical structure of the compounds present. In collaboration with the physiologist he must also explain such phenomena as the digestion and absorption of foods, respiration, the oxidation or catabolism of food materials, muscular contraction, glandular secretion, growth, regeneration, reproduction and the conduction of nerve impulses. While a vast amount of progress has already been made in the study of these problems by scientists of all nationalities, it must be admitted that only the surface has been laid bare. Much remains to be done. We are today unable to explain fully a single one of the processes listed above, indeed concerning the majority of these processes our present explanations are admitted to be entirely inadequate.

The domain included under the term biological chemistry is an extensive one. Thus, the organic chemist who secks to explain the chemical structure of proteins, phosphatides, bile pigments, or polysaccharides, can be said to be working in biological chemistry. The same thing can also be said of the analytical chemist who perfects new or more rapid

Vil vill INTRODUCTION methods for the analysis of biological substances, or publishes analytical data dealing with the organic or inorganic constituents of blood, urine or tissue; of the physical chemist who explains vital phenomena in terms of osmotic pressure, surface tension, hydrogen ion concentration, or viscosity; of the colloid chemist who studies the colloidal properties of plant and animal tissues and fluids, the swelling of gels and the precipitation of proteins; of the dietitian who investigates the biological food values of individual proteins, or the isolation of vitamins; or of the worker in the field of animal calorimetry who measures the production of energy and studies the influence of various factors upon the metabolic rate.

Closely related to physiological chemistry is the science of pathological chemistry, which concerns itself with the effect of disease upon the chemistry of the organism. The recent discovery of insulin and its use in diabetes mellitus is a noteworthy example of research in this and in closely allied fields. The isolation of adrenalin and thyroxin and the preparation of active extracts of the pituitary, of the ovaries and of the parathyroid glands, followed by investigation of the influence of these substances upon normal and diseased animals, are instances of what is being accomplished in the field of endocrinology, a subject of interest to physiologist and biochemist alike.

The Importance of Biological Chemistry.—The courses in biological chemistry offered in the curricula of our colleges have been devised largely for the student in medicine, but there are other fields, such as clinical analysis, dietetics, bacteriology, animal husbandry and dairy industry, wherein a substantial knowledge of the fundamental principles of biological chemistry can be said to be indispensible. Whereas the medical student of a generation ago was required to possess no more than a minimal knowledge of inorganic and organic chemistry, the medical student of the

INTRODUCTION ix present day studies inorganic, organic, analytical, and not infrequently physical chemistry, before admission to the first year of medical work. The proportionate number of hours devoted to biological chemistry during the first year of medicine indicates that this study is regarded as one of the most important of the medical sciences. Moreover the relative number of hours is being increased from time to time.

Biochemical Reactions.—All living things have been found to be composed of one or more cells. In consequence of this fact the cell has been taken as the unit of the organism. Chemically the cell is composed of such materials as proteins, carbohydrates, fats, phosphatides and cerebrosides; of extractive substances, such as creatin, creatinin, urea, amino acids and uric acid; and finally of inorganic salts, containing the cations, sodium, potassium, calcium, magnesium and iron and the anions, chloride, phosphate, carbonate, bicarbonate and sulphate. In many cases we find that these various constituents are chemically united with one another. Thus proteins often contain carbohydrate groups, the cerebrosides are complex fats which contain sugars and nitrogenous bases, and the proteins existing in protoplasm are always found to be united either with inorganic cations or anions. Of these compounds a certain number are crystalloids, while others, the proteins, phosphatides and higher carbohydrates, are known as colloids. The presence in plants and animals of compounds of colloidal nature, compounds which exist as gels and sols, which refuse to crystallize except in rare instances, and which are labile in nature and difficult to purify, has considerably increased the difficulties with which the biochemist is obliged to contend. However, the physical chemist and the colloid chemist have made notable progress in this field in recent years.

Chemical reactions are continually taking place within x INTRODUCTION the living cell. For the most part these reactions consist of oxidation, reduction, hydrolysis and dehydrolysis, or esterification, but a great many other reactions occur besides these. The sum of all of the reactions occurring in the cell is called metabolism. The oxidative reactions are included under the term catabolism and those reactions of a synthetic, or constructive nature are included under the term anabolism. Metabolism is always in part catabolic and in part anabolic. The essential difference between the plant and the animal is that the reactions of the former are to a large degree anabolic, while the reactions of the latter are, for the most part, catabolic. The plant cell containing chlorophyll has the power to synthesize carbohydrate from carbon dioxide and water, under the influence of sunlight, and to synthesize amino acids, when supplied in addition with such simple raw material as certain inorganic salts. Power to carry on synthetic reactions of this sort is not possessed by the animal cell. The animal cell is incapable of storing the energy of sunlight and is, therefore, obliged to depend either directly, as in the case of herbivora, or indirectly, as in the case of carnivora, upon the plant for its supply of energy, as well as for its supply of the majority of the amino acids. The animal does possess synthetic ability in certain directions, however, and to a very considerable degree. For example, any one of the cells from the liver can build and repair itself; can synthesize fibrinogen, glycogen, bile pigments and bile acids; can form urea from ammonium carbonate; can convert fructose and galactose into glucose; can convert glucose, or some degradation product of glucose, into fat; can detoxicate a great variety of poisonous substances; can form antitoxins; and can undoubtedly perform many other kinds of chemical work of a synthetic nature.

Methods of the Biological Chemist.—In attacking the complex and difficult problems that confront him the bio-

INTRODUCTION x1 chemist is obliged to resort to a variety of methods of experimentation and to take the utmost advantage of all improvements and advances achieved in the different fields of chemistry, physics, biology and the medical sciences. In some cases the hospital is able to provide opportunity and material for study, in other instances animal experimentation has been found to be the best and indeed the only means of solving some problem. Of the numerous methods used by the experimentalist a few examples are:

1, Chemical analysis of plant and animal tissues and fluids.

2. Search for new and as yet undiscovered plant and animal compounds.

3. Study of metabolic processes.

4. Study of hormones and their action.

5. Perfusion of surviving organs.

6. Feeding animals certain chemical compounds and observing what end product has been eliminated in the urine.

7. Study of the mechanics of enzyme action.

8. Study of the regulatory mechanism by which the body preserves its constancy of composition and reaction.

9. Feeding experiments to establish the nutritive value and vitamin content of foods.

Besides working with the test tube and the pipette, the colorimeter, the centrifuge and the analytical balance, the biological chemist is not unwilling to make use of the microscope, the ultra-microscope, the spectroscope, the animal calorimeter and the x-ray tube. Even the moving-picture machine and the radio have been recently pressed into service.

Biochemical Literature.—Biochemical literature can be divided into four types: text books, monographs, original articles and abstracts.

Such text books as Hammarsten and Hedin’s “Physioxll INTRODUCTION logical Chemistry,” Mathews’ “Physiological Chemistry” and Morse’s “Applied Biochemistry” are recommended to students because these volumes give a very complete presentation of the subject and include many topics that have been omitted from the present book. The text books of Mathews and Morse contain laboratory experiments and analytical methods as well as lecture material. For laboratory manuals the student is especially advised to consult Hawk’s “Practical Physiological Chemistry” and Folin’s “Laboratory Manual of Physiological Chemistry.” These two manuals contain a rather complete list of the analytical methods most frequently employed in the analysis of urine and blood.

The elementary student should not remain content with the study of text books, but should soon turn his attention to monographs. Fortunately there exists a large number of monographs dealing with a variety of biochemical topics. The monographs edited by Plimmer and Hopkins will be found especially helpful. A number of excellent monographs can be found in the “Physiological Reviews.”

Original articles in English are to be found in “The Journal of Biological Chemistry,’ “The Journal of the American Chemical Society,” “The Biochemical Journal,” “The American Journal of Physiology,” “The Journal of Physiology,” “The Journal of General Physiology,” “The British Journal of Experimental Biology,” “The Journal of the American Medical Association” and other journals not included in this list. The two most important German periodicals are possibly: “Zeitschrift fiir physiologische Chemie” and “Biochemische Zeitschrift.”

Abstracts are valuable largely for the purpose of finding out whether the original article is likely to contain matter of interest in connection with a certain topic. Abstracts of chemical and biological nature appear in the “Chemical Abstracts” of the American Chemical Society, in “The Pro-

INTRODUCTION Xi ceedings of the Society for Experimental Biology and Medicine,” in “Physiological Abstracts,” and “Biological Abstracts.” The index volumes of “Chemical Abstracts” will be found especially valuable for the beginner who does not know what journals to consult for articles bearing upon some specific topic.

Contents

PREFACE

Definition of Biological Chemistry.................. Aims and Ideals of Biological Chemistry. ........... Wteniaiacon One CCleN Cece, coy Foe obo hs cgi ok ae Importance of Biological Chemistry................ PSVOCMCINIC ALR CACHIONG 2 hie ict opendi afeo- accre cis. sie bu 5 se sores Methods of the Biological Chemist................. Brsoneuutal, Lataraire: <2 ie eo Sco ee es