Interheavy disulfide bridge in immunoglobulin G (IgG) reacting with dithionitrobenzoate. A unique feature in serum proteins.

Immunoglobulin G (IgG) of many species contains 'labile' disulfide bonds (SS*), which within 24 h undergo a disulfide exchange with dithionitrobenzoic acid (NBSSBN). Aims of the present study were to detect directly this type of SS* groups by means of 14C-labelled NBSSBN, and to investigate its possible presence in other serum proteins. NBSSBN reacts during the first 30 min of incubation with free SH groups, and thereafter with the sulfur atoms of SS* groups. The latter reaction reaches equilibrium after 24 h. The total of thionitrobenzoate residues (NBS) bound to IgG is called 'sigma S' and represents both SH and SS*. The results can be summarized as follows: (1) The measurement of the binding of 14C-NBSSBN gave identical sigma S values with IgG from humans and mice, as compared to the detection with the unlabelled reagent, which is based on the photometric determination of liberated NBS anions; whereas with IgG from rats some differences were observed which were ascribed to different batches of animals investigated; (2) experiments with electrophoretically separated serum proteins revealed only the gamma-globulins strongly binding 14C-NBSSBN in addition to the 30 min reaction, which indicates that SS* is confined to the gamma-globulin fraction; and (3) the significant decrease of sigma S in association with malignant tumors in man and animal models, which was previously described to be due to a specific alteration of the IgG subclass pattern, was likewise detected with the radiometrical method. Previous studies have identified SS* as one of the two inter-heavy disulfide bridges in IgG1, and possible implications of this group in specific functions of IgG1 are discussed.

Reactive disulfide bonds in immunoglobulin G. A unique feature in serum proteins of different species.

A reactive disulfide bond (SS)* was detected and characterized in IgG of humans, rats and mice by virtue of disulfide interchange with dithionitrobenzoate. (SS)* was found exclusively in human IgG1 and rat IgG2b. In human IgG1 (SS)* was identified as the upper one of the two interheavy bridges in the hinge, where it appears to take part in complement activation. The biological significance of (SS)* in IgG was underlined by the fact that no other serum proteins were found to exhibit a similar reactivity.

Spinal cysticercosis. Case report and review.

Cysticercosis is the commonest parasitic disease to affect the central nervous system (CNS). According to the World Health Organisation (1988), more than 2.5 million people worldwide are infected. Neurocysticercosis (NCC) is caused by the encysted larval form (porcine tapeworm) of Taenia solium (Cysticerus cellulosae). The ways in which the eggs of T Solium penetrate the CNS are illustrated in Table I. Involvement of the spinal cord in NCC varies between 1% and 5%. The isolated medullary form is very rare, only 50 cases having been reported up to 1988. The appearance of a spinal cord compression syndrome (SCCS) is unusual and late, according to reported series, the largest being that of Sotelo with 753 cases of NCC, including 10 causing SCCS, corresponding to 1.4%; also the classic Dixon and Lipscomb series of 450 NCC with only one patient with SCCS.

Labile disulfide bonds and free thiol groups in human IgG. I. Assignment to IgG1 and IgG2 subclasses.

The content of free SH groups (about 0.24) and labile S-S bonds (about 0.64) per mole human IgG can be differentially determined by the reaction with 5,5'-dithio(2,2'-dinitro)benzoate (DTNB) for 30 min and 24 h, respectively. Highly significant linear correlations were found between the number of labile S-S and the percentage of IgG1, and the number of free SH and the percentage of IgG2 of the total IgG fraction. It is concluded that the IgG1 molecule contains one S-S bond which is opened during the 24 h interaction with DTNB by a disulfide exchange reaction. This was also confirmed by the investigation of pure monomeric IgG1. The splitting of this bond does not alter molecular weight, antigenic properties or antigen binding activity, but reduces significantly the complement binding activity of IgG. On the other hand, one free SH group could be found in the IgG2 molecule. Changes have been observed in SH and S-S levels of total IgG in patients with various malignant diseases that are to be explained by corresponding changes of the percentages of IgG1 and IgG2.

Free thiol groups and labile disulfide bonds in the IgG fraction of human serum.

The IgG fraction was isolated from freshly taken blood serum of health persons (male and female) by column chromatography on QAE-Sephadex. After 30 min incubation with DTNB (5,5'-dithio-(2,2'-dinitro)-benzoate) the average photometrically determined quantity of thio-anions was 0.24 +/- 0.02 SH/mole IgG. Since this result remained unchanged even after 24 h incubation with DTNB, interaction with masked thiol groups cannot be assumed. If, however, the serum was incubated with DTNB for 24 h and the IgG fraction then isolated and treated with thioglycolate, an average of 1.51 +/- 0.39 moles of thio-anions were liberated per mole of IgG. This indicates that on 24 h interaction with IgG, DTNB not only reacts with free SH groups, but also opens S-S bonds by a disulfide exchange reaction. The amount of thio-anions resulting from such opened disulfide bonds was calculated as the difference between 1.51 0.24, i.e., 0.64 S-S/mole IgG. This would be accounted for if approximately 54% of the IgG fraction is composed of a subfraction containing 1 labile disulfide bone per mole. The average of 1.51 thio-anions per mole IgG resulted from 130 single values with an essentially normal statistical distribution and standard deviation well within the usual biological range.

Quantification and localisation of SH-groups in human blood serum proteins.

The thiol groups of human blood serum proteins were determined after 24 hours interaction with dithionitrobenzoic-acid (DTNB) to an average of 538 +/- 60 mumol/l serum. After treatment of the serum with [35S]DTNB, autoradiograms of the protein elpherograms revealed two main peaks: The first with 63% of total activity, in the albumin region, corresponding to 0.60 SH/mol, the second with 23% of total activity, in the gamma-globulin range, corresponding to 2.2 SH/mol. After 30 minutes incubation with DTNB, or with p-chloromercuribenzoate (CMB), in freshly prepared pools of IgG only 0.2 SH/mol were found which is the expected value already known from the literature. Autoradiograms taken from serum protein elpherograms after interaction with [14C]CMB only show the main SH-peak in the albumin range. Thus it is concluded that the SH-peak in the gamma-globulin region after 24 hours incubation with [35S]DTNB is due to one highly labile S-S-bond which easily undergoes a disulfide exchange with DTNB.