Disulfides of the lutropin receptor

Affinity cross-linking of the lutropin receptor with 125I-human choriogonadotropin (hCG) on porcine granulosa cells produced four distinct homone-receptor complexes under reducing conditions. They contain 18-, 24-, 28-, and 34-kDa components (Ji, I., Bock, J. H., and Ji, T. H. (1985) J. Biol. Chem. 260, 12815-12821). Photoaffinity labeling and cross-linking produced 136-, 102-, and 74-kDa hCG-receptor complexes under reducing conditions and the 136-kDa complex under nonreducing conditions. In addition, the unreduced 102-kDa complex was seen in photoaffinity labeling but not in cross-linking. When the unreduced 136-kDa complex was reduced, the 102- and 74-kDa complexes were generated, indicating release of the 34- and the 28-kDa components in two steps. When the unreduced 102-kDa complex was reduced, the 74-kDa complex was produced, indicating the release of a 28-kDa component. The 74-kDa complex could not be reduced but was cleaved by alkaline treatment to produce the hCG alpha beta dimer. The results indicate that the 24-kDa component is released from the 74-kDa complex, since the apparent mass of the hCG alpha beta dimer on gels is 50 kDa. The 24-kDa component appears to be the initial site for photoaffinity labeling or cross-linking and to be disulfide linked to the 28-kDa component which is in turn disulfide linked to the 34-kDa component. These intercomponent disulfides exist in some receptors but not all. Formation of the disulfide-linked 136-kDa band required the presence of a sulfhydryl-blocking agent, N-ethylmaleimide. In particular, the 34-kDa component was vulnerable to reduction. There was no significant evidence of disulfides between the hormone and any of the receptor components.     

Isolation and characterization of a new 40-kilodalton protein from bovine cardiac muscle

A new protein having a subunit weight of 40,000 has been purified from myosin-extracted bovine cardiac myofibrils. Its amino acid composition and isoelectric point are distinct from actin, eu-actinin, and a variety of sarcoplasmic proteins of similar size. Affinity-purified antibodies made to this protein only react with a single 40-kDa protein band from cardiac myofibrils on immunoblots. The anti-40-kDa protein also shows cross-reactivities with cardiac myofibrils from rabbits, rats, and chickens. Immunofluorescence studies demonstrate that the 40-kDa protein is localized at the Z-bands of cardiac myofibrils and at the intercalated discs. The antibody did not react with skeletal muscle myofibrils by immunofluorescence or immunoblotting. It appears that the 40-kDa protein may play a role in the strong attachments between adjacent myofibrils in cardiac muscle.     

Independence of exercise hyperpnea and acidosis during high-intensity exercise in ponies

We investigated arterial PCO2 (PaCO2) and pH (pHa) responses in ponies during 6-min periods of high-intensity treadmill exercise. Seven normal, seven carotid body-denervated (2 wk-4 yr) (CBD), and five chronic (1-2 yr) lung (hilar nerve)-denervated (HND) ponies were studied during three levels of constant load exercise (7 mph-11%, 7 mph-16%, and 7 mph-22% grade). Mean pHa for each group of ponies became alkaline in the first 60 s (between 7.45 and 7.52) (P less than 0.05) at all work loads. At 6 min pHa was at or above rest at 7 mph-11%, moderately acidic at 7 mph-16% (7.32-7.35), and markedly acidic at 7 mph-22% (7.20-7.27) for all groups of ponies. Yet with no arterial acidosis at 7 mph 11%, normal ponies decreased PaCO2 below rest (delta PaCO2) by 5.9 Torr at 90 s and 7.8 Torr by 6 min of exercise (P less than 0.05). With a progressively more acid pHa at the two higher work loads in normal ponies, delta PaCO2 was 7.3 and 7.8 Torr by 90 s and 9.9 and 11.4 Torr by 6 min, respectively (P less than 0.05). CBD ponies became more hypocapnic than the normal group at 90 s (P less than 0.01) and tended to have greater delta PaCO2 at 6 min. The delta PaCO2 responses in normal and HND ponies were not significantly different (P greater than 0.1).(ABSTRACT TRUNCATED AT 250 WORDS)     

Composition of cross-linked 125I-follitropin-receptor complexes

Both of the alpha and beta subunits of intact human follitropin (FSH) were radioiodinated with 125I-sodium iodide and chloramine-T and could be resolved on sodium dodecyl sulfate-polyacrylamide gels. Radioiodinated FSH was affinity-cross-linked with a cleavable (nondisulfide) homobifunctional reagent to its membrane receptor on the porcine granulosa cell surface as well as to a Triton X-100-solubilized form of the receptor. Cross-linked samples revealed three additional bands of slower electrophoretic mobility, corresponding to 65, 83, and 117 kDa, in addition to the hormone bands. The hormone alpha beta dimer band corresponded to 43 kDa. Formation of the three bands requires the 125I-hormone to bind specifically to the receptor with subsequent cross-linking. Binding was prevented by an excess of the native hormone but not by other hormones. A monofunctional analog of the cross-linking reagent failed to produce the three bands. Reagent concentration-dependent cross-linking revealed that their formation was sequential; smaller complexes formed first and then larger ones. When gels of cross-linked complexes were treated to cleave covalent cross-links and then electrophoresed in a second dimension, 18-, 22-, and 34-kDa components were released, in addition to the alpha and beta subunits of the hormone.     

Leishmania mexicana pifanoi: in vivo and in vitro interactions between amastigotes and macrophages

Macrophages of the cell line J774 were used in a comparative study of virulence involving amastigote stages of Leishmania mexicana pifanoi isolated from macrophages (AMA-M) of the aforementioned cell line, amastigote forms grown in the UM-54-cell-free medium (AMA-C), and promastigote stages. The macrophage cultures were inoculated with AMA-M and AMA-C at the culture cell to parasite ratios of 1:3, 1:5, and 1:10. The macrophages were exposed to either kind of amastigotes for 24, 48, and 72 h. At the end of each of these periods, and for each dilution, the percentages of macrophages harboring the parasites within their cytoplasm and the mean numbers of intracellular parasite/macrophage were estimated on the basis of examination of 200 phagocytes. When either AMA-M or AMA-C were employed, after 24 h, the percentages of infected macrophages were, respectively, 84.5%, 89.0%, and 94.5% for the three aforementioned dilutions, the majority of the phagocytes containing 1-5 parasites. After 48- and 72-h exposures, the macrophages harbored 6-11 and 11-20 amastigotes/cell, respectively. Evidently intracellular multiplication of the amastigotes has taken place. In contrast to the results obtained with amastigote forms, after inoculations of the macrophages cultures with promastigotes at the dilutions previously used for amastigotes, only 48-78 phagocytes were found to contain intracellular stages within their cytoplasm. Many macrophages were parasite-free, especially when exposed to fewer promastigotes. Experiments in which 5 X10(6) promastigotes, AMA-M, or AMA-C were inoculated into the footpads of hamsters yielded the following results with regard to terminal footpad volumes: 1.57, 3.31, and 3.32 cm3, respectively. Evidently both kinds of amastigotes had equal virulence for hamsters; however, the promastigote stages were much les virulent for these experimental hosts.     

Geographical variability of alpha-1-antitrypsin alleles in China: A study on six Chinese populations

Summary Alpha-1-antitrypsin phenotypes of six Chinese Han populations (20°–45°N. latitude) were determined. The frequency of allele M2 increases from North to South China. The north-south change of M2 appears to be mainly at the expense of alleles M1 and M3. Geographical variability of other variants was also observed. In the northern populations, the most common variants are M4 and Etokyo; in the southern populations, Pweishi, a variant which can not be distinguished electrophoretically from Pyasugi. These results form a distribution pattern of alpha-1-antitrypsin alleles in China.     

接触二氧化硫后小麦叶片中逆境乙烯的生物合成

AVG和AOA强烈抑制二氧化硫处理小麦叶片中乙烯产生和ACC合成,对MACC的形成也有一定的抑制作用。CoGl_2明显抑制乙烯产生,而ACC大量积累,MACC含量则未因ACC增加而相应增加。DNP和CCCP也抑制乙烯产生,但前者引起ACC大量积累,后者引起ACC含量下降。CHI对乙烯产生和ACC形成均显示强烈的抑制作用,同时也明显抑制MACC形成。这表明小麦叶片接触SO_2引起的逆境乙烯也是循蛋氨酸→SAM→ACC→乙烯途径。