THE CATABOLISM OF HOMOLOGOUS AND HETEROLOGOUS 7S GAMMA GLOBULIN FRAGMENTS

The catabolism of homologous and heterologous 7S gamma globulin fragments obtained by pepsin and papain digestion was studied in rabbits, guinea pigs, and mice. The elimination from the circulation of I* labeled gamma globulin fragments was followed and the urinary excretion of the total and protein-bound I* activity determined. Evidence is presented that the molecular structure responsible for the catabolism of 7S gamma globulin is located in papain fragment III. The elimination of papain fragment III was slow and closely related to the intact gamma globulin, whereas the pepsin fragment and papain fragments I and II were rapidly eliminated and catabolized in all species examined. Prolonged incubation with cysteine altered papain fragment III as shown by a rapid catabolism of a large portion of incubated fragment III within 24 hours after injection. Small amounts of intact RGG and RGG papain fragment III were excreted as protein-bound I* activity in the urine. On the other hand, large amounts of the pepsin fragment and papain fragments I and II of RGG were excreted as protein-bound I* activity in the urine. The possibility of a molecular structure present in papain fragment III, which may be responsible for tubular reabsorption in the kidney, is discussed. The rate of urinary excretion of fragments obtained from RGG was different from that of fragments obtained from gamma globulin of several other species. In general, small amounts of the pepsin fragment and papain fragment III obtained from gamma globulin other than RGG were excreted as protein-bound I* activity. The amounts of fragment I* excreted as protein-bound I* activity depended on the species in which it was injected, as well as the source of the gamma globulin. The rapid catabolism of the pepsin fragment and papain fragments I or II which bear antibody-combining sites suggest that their use for the prophylactic treatment of tetanus and diphtheria in man is limited.

CORROBORATION OF RECENT MODELS OF THE GAMMA-G IMMUNOGLOBULIN MOLECULE

The relationships between the polypeptide chains of γG immunoglobulin and fragments of the molecule produced by papain and pepsin have been investigated. Specific procedures were employed including peptide mapping of tryptic hydrolysates and analysis of molecules reconstituted from chains labeled with different iodine isotopes. By these means, the Fab fragment was shown unequivocally to consist of the light chain and a portion of the heavy chain, the Fd fragment. The Fc fragment was found to be comprised of the residual portions of the heavy chain. These findings support the gross arrangement of chains embodied in recent models of the γG immunoglobulin molecule. The present studies have also provided additional information on the susceptibility of γG immunoglobulin to proteolytic cleavage. It was found that the portion of heavy chains corresponding to the Fd fragment was extensively cleaved by papain.

PEPSIN DIGESTION OF RABBIT AND SHEEP ANTIBODIES. THE EFFECT ON COMPLEMENT FIXATION

7S sheep antibody is similar to 7S rabbit antibody, insofar as it too can be digested with pepsin to yield a 5S fragment still capable of precipitating homologous antigen. The 5S fragment from rabbit as well as sheep antibody is capable of fixing guinea pig complement. However, this fixation differs from the fixation by 7S antibody, since preformed antibody-antigen aggregates containing either sheep or rabbit 5S antibody fix only a maximum of 20 to 40 per cent of the total complement. The portion of complement which is fixable by the 5S preformed aggregates seems to be different from the remainder of the complement. Prior treatment of guinea pig serum with 5S washed preformed aggregates removes that portion of complement fixable by 5S antibody, and will leave the complement remaining unable to be fixed by further addition of 5S immune aggregates. Such absorbed complement, however, is as capable as is unabsorbed complement of being fixed by 7S antibody. The 5S sheep and rabbit antibody fixes the portion of complement which it is capable of fixing, as well as or better than the corresponding 7S antibody fixes the total complement. 5S preformed aggregates are broken down by treatment with cysteine, and their complement-fixing ability is lost.

THE ROLE OF DISULFIDE BONDS IN THE COMPLEMENT-FIXING AND PRECIPITATING PROPERTIES OF 7S RABBIT AND SHEEP ANTIBODIES

The number of total disulfide bonds in rabbit and sheep 7S gamma globulin, before and after treatment with 2-mercaptoethanol, has been measured by amperometric titration. Mercaptan reduction could diminish the complement-fixing efficiency of 7S rabbit gamma globulin by no more than 90 per cent without any significant decrease in maximal complement-fixing ability. This was associated with the reduction of only 7 disulfide bonds, including 1 interchain disulfide bond [S—S₍₁₎]. The reduction of 7 disulfide bonds in 7S sheep gamma globulin was associated with a 64 per cent decrease in complement-fixing efficiency, while reduction of 10 to 11 disulfide bonds decreased the complement-fixing efficiency by 90 per cent. Reduction of more disulfide bonds was not associated with any further decrease in complement-fixing efficiency, nor of any decrease in maximal complement-fixing ability. The reduction of more than 10 to 11 disulfide bonds in 7S rabbit and sheep gamma globulins was associated with a decrease in precipitating ability. The disulfide bonds which are more labile to mercaptan reduction appear to be associated with complement-fixing efficiency while the disulfide bonds which are more resistant to mercaptan reduction appear to be associated with precipitating ability. The measurement of interpolypeptide chain disulfide bonds has been discussed. One easily reduced interchain disulfide bond [S—S₍₁₎] appears to be important for the complement-fixing efficiency of 7S rabbit antibody. The integrity of this same bond is essential for the precipitating ability of 5S rabbit antibody and may also be important for its complement-fixing ability.

PEPSINOGEN B: THE ZYMOGEN OF PEPSIN B

1. Pepsinogen B, the precursor of pepsin B, has been isolated by ion-exchange chromatography and gel filtration from neutral extracts of pig gastric mucosa. The material possesses potential activity against acetyl-l-phenylalanyl-l-di-iodotyrosine and against gelatin but has little, if any, potential activity against haemoglobin. 2. The material appears homogeneous in the ultracentrifuge, but on gel filtration and on electrophoresis in starch gel it is shown to be contaminated with a small amount of material having potential activity against haemoglobin. On electrophoresis in starch gel also the material is shown to contain about equal amounts of two major components, both of which have potential activity against the synthetic substrate. Pepsin B has also been shown to contain two active components by electrophoresis under the same conditions. 3. The zymogen is similar to pepsinogen and pepsinogen C in its molecular weight and general physico-chemical properties, but differs from these zymogens in the nature of its N-terminal residues. It is possible that one of the components contains 1 mole of bound phosphate/mole. 4. The material is activated rapidly at pH2 and more slowly at pH4. At both pH values the kinetics of the activation reaction are complex.

STUDIES ON THE MUCIN DERIVED FROM HUMAN COLLOID BREAST CARCINOMA

1. A non-diffusible mucoid, showing a single peak in the ultracentrifuge, was isolated from human colloid breast carcinoma by treatment with trypsin and pepsin. The material contained threonine, leucine (isoleucine), valine, proline, glycine and glutamic acid in the approximate molar proportions 5:1:1:2:1:1. Smaller amounts of aspartic acid and serine were also found. For each 5 threonine residues, 6 N-acetylgalactosamine and 3-4 galactose residues were present. 2. The mucoid possessed reducing properties by the Park & Johnson (1949) procedure; these were attributable to the action of mild alkali, as employed in this procedure. Mild alkaline treatment by the Aminoff, Morgan & Watkins (1952) procedure gave rise to a diffusible N-acetylgalactosamine chromophore that gave an enhanced colour with Ehrlich's reagent. That galactosyl-(1-->3)-N-acetylgalactosamine residues were liberated was supported by periodate studies. 3. Alkaline liberation of hexosamine residues was accompanied by a specific destruction of threonine. After 40 min. at 100 degrees in 0.18 n-lithium hydroxide, both moieties had almost completely disappeared from the ninhydrin-positive components formed on subsequent acid hydrolysis. Glycine and alpha-oxobutyric acid were present in the acid hydrolysate, showing that both possible pathways of a beta-elimination reaction were involved. Formation of diffusible peptide on very mild alkaline treatment was attributable to the rupture of the original peptide core, necessitated by the second of these two pathways. 4. Hydroxamate formation on treatment with hydroxylamine showed the presence of carbohydrate linkage to glutamic acid or aspartic acid residues or both. This could account for the single N-acetylgalactosamine residue not linked to threonine. 5. The native mucin contained sialic acid, which was cleaved by the acid environment used in the treatment with pepsin. A statistical model of the mucin would require each prosthetic group to be linked, via N-acetylgalactosamine, to threonine, which would occupy every alternate position among the amino acids in the peptide core.

HYDROLYSIS OF PROTEINS AND NUCLEIC ACIDS BY LANCEFIELD GROUP A AND OTHER STREPTOCOCCI

Deibel, R. H. (American Meat Institute Foundation, Chicago, Ill.). Hydrolysis of proteins and nucleic acids by Lancefield group A and other streptococci. J. Bacteriol. 86:1270-1274. 1963.-Classically, group A streptococci have been considered to be nonproteolytic in spite of the observation that a proteinase is produced in broth cultures. When tested by the plate method, it was observed that 78% of 47 strains were proteolytic when the cultures were incubated anaerobically. Some strains hydrolyzed gelatin aerobically; however, the hydrolysis of casein and pepsin required anaerobic conditions of growth. Other proteins hydrolyzed included wheat gluten and a beef-muscle preparation. The hydrolysis of bovine serum albumin, lactalbumin, sheep plasma, and lysozyme was not detected in plate cultures. The hydrolysis of deoxyribonucleic acid and ribonucleic acid was characteristic of the majority of the strains. Unlike the proteolytic activity, the nucleolytic activity was independent of oxygen tension. Other streptococci were screened for hydrolytic activity; among these strains, only the single strain of Streptococcus sanguis tested possessed proteolytic activity. Deoxyribonuclease activity was observed in "animal" but not "human" group C strains, and in some strains of groups G and L.

BETA-HEMOLYTIC STREPTOCOCCI WITH GROUP A AND TYPE II CARBOHYDRATE ANTIGENS

Jablon, James M. (National Children's Cardiac Hospital, Miami, Fla.), Betty Brust, and Milton S. Saslaw. beta-Hemolytic streptococci with group A and type II carbohydrate antigens. J. Bacteriol. 89:529-534. 1965.-Ten strains of beta-hemolytic streptococci with unusual somatic antigens were isolated from excised tonsils or throat cultures or both. Acid extracts of these strains reacted with commercial group A and group F antisera, but gave no reaction when tested with 35 type-specific group A antisera. Serum cross-absorption and agar-gel diffusion studies established the identity of the reactive antigens as the specific carbohydrates of group A and of type II. The latter antigen has been found in many strains of group F streptococci. The organisms do not possess the group-specific carbohydrate of group F, and the reaction with the commercial group F antiserum is due to the presence of type II antibody in the antiserum. The organisms give a stronger reaction to fluorescein-conjugated type II antiserum than to group A. However, the organisms have only one group-specific carbohydrate, that of group A, and, tentatively, should be classified as such.

STRUCTURAL STUDIES OF HUMAN 7S GAMMA-GLOBULIN (G IMMUNOGLOBULIN). FURTHER OBSERVATIONS OF A NATURALLY OCCURRING PROTEIN RELATED TO THE CRYSTALLIZABLE (FAST) FRAGMENT

1. Detailed physical, chemical, and immunologic studies of a protein closely related to the Fc fragment and heavy chain of G immunoglobulin (IgG), and elaborated by a subject with a lymphoproliferative disorder are presented. 2. The protein, which has a molecular weight of 51,000, was cleaved into two half molecules by reduction and alkylation. 3. The protein has few if any of the antigenic determinants of the antigen-binding (Fab) papain fragment of IgG, and has a striking similarity in its antigenic properties to the Fc fragment. 4. Fingerprint patterns resemble those of the crystallizable (Fc) fragment, and lack several peptides found in the heavy chain. 5. These findings suggest that the Fc fragment may be a real structural unit of IgG, and raise the possibility of the existence of three different types of polypeptide chains in G immunoglobulin.

PROPERTIES OF VARIOUS ANTI-GAMMA-GLOBULIN FACTORS IN HUMAN SERA

The serological and physicochemical properties of the following three forms of human anti-γ-globulin factors were compared: (a) rheumatoid factors; (b) Milgrom type anti-γ-globulin factors; and (c) factors directed against an antigen in human γG-globulin that is hidden in the intact molecule and revealed by enzymatic digestion at low pH. The property common to these factors is ability to interact with human γG-globulin; they are distinguishable because they react with different antigenic groups on this molecule. In all of five sera, the Milgrom type anti-γ-globulin factors were γM-globulins. They reacted with various human γG-globulin antibodies but failed to interact with γM-globulin type antibodies in agglutination and absorption experiments. When isolated from other anti-γ-globulin factors, they agglutinated red cells coated with intact anti-Rh antibodies, but failed to react with cells cells coated with pepsin-digested anti-Rh antibody. These observations indicate that the agglutinator reacts with the crystallizable, inert fragment of γG-globulin. Anti-γ-globulin activity directed against an antigen in human γG-globulin revealed by pepsin digestion was demonstrated in γG-, γA-, and γM-globulins. This anti-γ-globulin factor could be absorbed by antigen-antibody precipitates containing human antibody, which shows that the hidden antigen in human γG-globulin is revealed not only by enzymatic digestion at low pH, but also when γG-globulin is present as antibody in an antigen-antibody precipitate. Rheumatoid factors and Milgrom type anti-γ-globulin factors were also absorbed by antigen-antibody precipitates containing human antibody. The results indicate that the three distinct forms of antiγ-globulin factors may all be produced as a result of antigenic stimulation by autologous antigen-antibody complexes.