Streptococcal Fc receptors. II. Comparison of the reactivity of a receptor from a group C streptococcus with staphylococcal protein A

The reactivity of a soluble Fc receptor from a group C streptococcus ( FcRc ) was compared antigenically and functionally with the staphylococcal Fc receptor, protein A. Protein A and FcRc were found to inhibit each others' binding to the Fc region of human IgG, indicating that they bind to sites that are in close proximity on the Fc region of human IgG. The two bacterial Fc receptors were antigenically unrelated. Differences were observed in the species and subclass reactivity of the two receptors. The patterns of binding of protein A and FcRc under various conditions suggested that these receptors reacted with distinct regions on the Fc region of immunoglobulins. FcRc bound more efficiently to goat, sheep, and cow IgG, protein A bound more efficiently to dog IgG, and neither receptor bound to rat IgG. Differences were also observed in the reactivity towards human IgG subclasses. The FcRc bound to all samples of the four human IgG subclass standards. Protein A bound to IgG1, IgG2, and IgG4, and to one of two IgG3 myeloma proteins tested. The reactivity of our soluble FcRc corresponds to a type III streptococcal Fc receptor classified by the reactivity of intact bacteria.     

Streptococcal Fc receptors. I. Isolation and partial characterization of the receptor from a group C streptococcus

A receptor for the Fc region of immunoglobulin G was extracted from a group C streptococcus, purified and physicochemically characterized. The Fc receptor was extracted in high yield by lysis of the bacteria after infection with bacteriophage. The soluble receptor was purified to functional homogeneity by sequential chromatography on cellulose phosphate, DEAE, and selective elution from a column of immobilized human IgG. Four hundred micrograms of the functionally pure protein was obtained per gram (wet weight) of bacteria extracted. The affinity-purified receptor was functionally homogeneous in binding to the Fc region of human IgG; however, the product was heterogeneous on both non-denaturing and SDS polyacrylamide gels. Four major protein bands were observed, with the predominant form of the Fc receptor having an m.w. of 64,000 daltons. Antibody prepared against the major Fc receptor protein ( FcRc -II) was capable of reacting with all the fractions and completely inhibiting functional activity. The results of the competitive binding studies suggest that the purified Fc receptor behaves as a single receptor, and that the differences in charge and size were probably due to covalently bound cell wall constituents.     

A further study on the dietary-regulated biosynthesis of high-sulphur wool proteins

When the diet of sheep is supplemented by the infusion of sulphur-containing amino acids or casein into the abomasum, the newly synthesized wool shows characteristic changes in its amino acid composition, with significant increases in cystine, proline and serine and decreases in aspartic acid and phenylalanine. This modification seems to be due entirely to an alteration in the overall composition of the high-sulphur proteins and to an increase in their proportion in the fibre. These variations are not the result of a change in the composition of individual proteins, but are due to alterations in their relative proportions and to the initiation of the synthesis of `new' proteins, many of which are extremely rich in cystine. It is suggested that the heterogeneity of the high-sulphur proteins may be due, in part, to similar changes in composition caused by natural variations in the nutrition of sheep.     

The chromosomes ofAzima tetracantha (Salvadoraceae)

Azima tetracantha has an asymmetrical karyotype with large chromosomes and a large amount of heterochromatin. The haploid number (n = 11) may represent the base number of the family. However, a possible secondary origin of this base number is also considered.     

Band-specific localization of the microsatellite at D13S71 by microdissection and enzymatic amplification.

Microsatellite DNA consists of tandemly repeated simple DNA sequence motifs, the number of these repeats being polymorphic. These recently described polymorphisms are ubiquitously distributed throughout the human genome and are highly informative, making them ideal markers for linkage analysis. Physical localization of these microsatellites is an important prerequisite for aligning physical and genetic maps. We have physically mapped the microsatellite at D13S71, which has previously been assigned to chromosome 13. Band-specific mapping of D13S71 to the distal part of band 13q32, near 13q33, was achieved by microdissection of GTG-banded chromosomes and subsequent enzymatic amplification with a heminested PCR approach. Analysis of a panel of somatic cell hybrids confirmed this localization. The technique presented may also be useful in a variety of complex mapping situations and whenever the precise localization of very small (as small as 70 bp) DNA probes is necessary.     

A region of tissue plasminogen activator that affects plasminogen activation differentially with various fibrin(ogen)-related stimulators.

The dissolution of blood clots by plasmin is normally initiated in vivo by the activation of plasminogen to plasmin through the activity of tissue plasminogen activator (t-PA). The rate of plasminogen activation can be stimulated several orders of magnitude by the presence of fibrin-related proteins. Here we describe the kinetic analysis of both recombinant human t-PA (wild-type) and a t-PA variant produced by site-directed mutagenesis in which the original sequence from amino acids 296 to 299, KHRR, has been altered to AAAA. This tetra-alanine variant form of t-PA, K296A/H297A/R298A/R299A t-PA, we refer to as "KHRR" t-PA here. The plasminogen activating kinetics of wild-type t-PA (Activase alteplase) showed a catalytic efficiency which changed over 100-fold dependent on the stimulator in the assay. The lowest rate was in the absence of a stimulator. The following stimulators showed increasing ability to accelerate the catalytic efficiency of the reaction: fibrinogen, fragments of fibrinogen obtained by digestion with plasmin, fibrin, and slightly degraded fibrin. This increase in efficiency was driven primarily by decreases in the Michaelis constant (KM) of the reaction, whereas the catalytic rate constant (kcat) of the reaction did not change significantly. The "KHRR" variant of t-PA displayed novel kinetics with all stimulators tested. In the absence of a stimulator or with the poorer stimulators (fibrinogen and fibrinogen fragments), the KM values of the reaction with Activase alteplase and "KHRR" t-PA were similar. The kcat however, was lower with "KHRR" t-PA than with wild-type t-PA.(ABSTRACT TRUNCATED AT 250 WORDS)