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P Bai

Publications and source records attributed to P Bai.

15 recordsLinked to original sources
PubMed2000

Side chain accessibility and dynamics in the molten globule state of alpha-lactalbumin: a (19)F-NMR study.

The molten globule state of alpha-lactalbumin (alpha-LA) has been considered a prototype of partially folded proteins. Despite the importance of molten globules in understanding the mechanisms of protein folding and its relevance to some biological phenomena, site-specific information on the structure and dynamics of a molten globule is limited, largely because of the high conformational flexibility and heterogeneity. Here, we use selective isotope labeling and (19)F NMR to investigate the solvent accessibility and side-chain dynamics of aromatic residues in the molten globule of alpha-LA. Comparison of these properties with those of the native and unfolded protein indicates that the alpha-LA molten globule is highly heterogeneous; each residue has its unique solvent accessibility and motional environment. Many aromatic residues normally buried in the interior of native alpha-LA remain significantly buried in the molten globule and the side-chain dynamics of these residues are highly restricted. Our results suggest that hydrophobic and van der Waals interactions mediated by the inaccessible surface area could be sufficient to account for all the stability of the alpha-LA molten globule, which is approximately 50% of the value for the native protein.

Fluorine↗
PubMed1998

Contribution of individual residues to formation of the native-like tertiary topology in the alpha-lactalbumin molten globule.

Molten globules are partially folded forms of proteins that have native-like secondary structure and a compact geometry, but often without rigid, specific side-chain packing. Recently, the molten globule of alpha-lactalbumin (alpha-LA) has been shown to adopt a native-like tertiary topology, mainly localized in the alpha-helical domain. This native-like topology is reflected by the high effective concentration (Ceff) for formation of the 28-111 disulfide bond, which is approximately 10 to 40 times higher than the Ceff for formation of any non-native disulfide bond in the alpha-helical domain. In order to understand the mechanism for formation of the native-like tertiary topology, we substituted alanine for each of the 23 buried residues in the alpha-helical domain of alpha-LA and determined the effect of these substitutions on the Ceff for formation of the 28-111 disulfide bond. Our results indicate that a subset of hydrophobic residues is most important for formation of the native-like topology. These residues form a densely packed core in the three-dimensional structure of alpha-LA. In contrast, the less important residues consist of both hydrophobic and hydrophilic amino acids located at peripheral positions. These results suggest that a relatively small number of hydrophobic residues may be sufficient for specifying the overall structure of a protein during early stages of protein folding.

Cysteine↗
PubMed1997

[A clinical analysis of 153 uterine sarcomas].

OBJECTIVE: To evaluate the prognostic factors and treatment methods of 153 uterine sarcomas. METHODS: 153 cases of the uterine sarcoma were eligible for this retrospective study. Of the 153 cases, 48 were leiomyosarcomas, 47 mixed mesodermal sarcomas, 37 endometrial stromal sarcomas, 8 carcinosarcomas, 4 sarcoma botryoides, 1 fibrosarcoma, and 8 malignant lymphomas. 81 cases were in stage I, 11 stage II, 33 stage III and 11 stage IV. 38 cases were treated by surgery alone, 24 by surgery combined with radiation therapy, 50 by surgery plus chemotherapy, 23 by surgery plus radiation therapy and chemotherapy, 4 by radiation therapy alone, 3 by chemotherapy alone, and 11 by radiation therapy plus chemotherapy. RESULTS: The overall 5-year survival rate was 49.0%, and that of leiomyosarcomas, mixed mesodermal sarcomas and endometrial stromal sarcomas was 46.9%, 34.1% and 69.3% respectively (P < 0.01). The 5-year survival rate of lesions limited to the uterus (stage I + II), and that of pelvic cavity invasion (stage III) and distant metastases was 59.6%, 25.6% and 10.0% respectively (P < 0.01. When the uterus was smaller than a 3 months pregnant uterus, the 5-year survival rate was 49.9%. When the uterus size larger than a 3 months pregnant uterus, the survival rate was 18.8% (P < 0.05). Premenopausals surviving 5-year accounted for 56.3% and post-menopausal 28.9% (P < 0.01). CONCLUSIONS: The prognosis of uterine sarcoma is significantly associated with histologic type, clinical and surgico-pathological stage, uterine size and pre- or post-menopausal status. Radiation or chemotherapy alone is palliative. Postsurgical adjuvant radiotherapy significantly decreased vaginal and pelvic recurrences rates. A combination of surgery, radiotherapy and chemotherapy can reduce pelvic recurrence as well as enhance survivals.

Adolescent↗
PubMed1995

[Primary malignant lymphoma of the female genital tract clinical analysis of 15 cases].

OBJECTIVE: To review fifteen cases with primary malignant lymphoma of the female genital tract at Cancer Hospital, Chinese Academy of Medical Sciences from 1980 approximately 1994. METHODS: This is a clinical retrospective analysis. There were 7 cases of lymphoma originating in the cervix, 2 in the vagina, 3 in the ovary, 1 in the vulva, endometrium and pelvic cavity respectively. All of the 15 cases were given combination therapy. 3 ovarian lymphoma were treated by surgery and chemotherapy, 2 cervical lymphoma and 1 endometrial lymphoma by surgery, chemotherapy and radiotherapy, 1 pelvic lymphoma by surgery and radiotherapy, others by radiotherapy and chemotherapy. RESULTS: Two patients are living more than 5 years, 3 patients more than 3 years. 4 patients were followed up for less than 2 years and 6 patients relapsed or died. CONCLUSIONS: The prognosis of ovarian lymphoma is worse than that of other genital sites. Combined and sequential chemotherapy-radiotherapy-chemotherapy is the proper treatment sequence for lymphoma of the cervix, vagina and vulva. Extensive chemotherapy may be an appropriate choice for highly malignant pathological type. Radiation should be given early for large cervical lymphoma.

Adult↗
PubMed1994

[Operative treatment for vulvar cancer by different methods].

A retrospective analysis of 88 patients with vulvar cancer treated by radical vulvectomy and groin lymphadenectomy from July, 1958 to December, 1990 is presented. 88 cases are divided into two groups based on different operative methods: the enbloc group (25 cases) and the non-enbloc group (63 cases). No significant statistic differences are found in the 5-year survival rates (76.0% vs 79.8%) and the complications (erysipelas, lower extremity edema) between the two groups. The wound healing time is 14.4 days shorter in the non-enbloc group than enbloc group. Factors such as clinical staging, metastasis to the inguinal lymph nodes and histopathological classification are also investigated for correlation with the prognosis.

Adult↗
PubMed1993

Detection of antigens of Mycobacterium tuberculosis in patients of infertility by monoclonal antibody based sandwiched enzyme linked immunosorbent assay (ELISA).

A sandwich ELISA to detect specific protein antigens of Mycobacterium tuberculosis was developed by using polyclonal anti-BCG rabbit antibodies as the primary capture antibodies. The mycobacterial antigens were detected with horseradish peroxidase conjugated monoclonal antibodies (P 6) as secondary antibodies. The enzyme was detected by using 1,2 Phenylenediamine dihydrochloride (OPD) and Hydrogen peroxide as substrate. The antigen could be quantitated through linear regression analysis with lower detection limit of 1.25 micrograms/ml. 50 consecutive cases of infertility were examined by laparoscopy and tested for the presence of the antigen in the serum. Mycobacterial antigen could be detected in 9 of the 12 cases with definitive diagnosis of tuberculosis, 5 of the 23 where the diagnosis of tuberculosis was probable and in only 1 of 15 patients who had no laparoscopic abnormalities indicative of tuberculosis.

Adult↗
PubMed1992

Glycation alters collagen fibril organization.

Incubation of rat tail tendon in 0.2M ribose results in accelerated non-enzymatic glycosylation of collagen, with the formation of fluorescent cross-links between molecules and decreased solubility. Electron micrographs of tendon cross-sections show an increased fibril packing density with increasing degrees of glycation. After a one-week incubation in ribose, every fibril appears in close contact with all of its neighbors, and the packing density has increased to 76%, from a value of 62% in controls. Irregular diameters and fusion of fibrils also are seen. All of the fibrils in a bundle appear to become cross-linked together, creating a larger stress bearing unit. This model is consistent with stress-strain curves showing a large increase in tensile stress and stiffness after a one-week incubation period in ribose. The diameters of the collagen fibrils increase in size in glycated tendon. We hypothesize larger diameters result from an increased resistance to shrinkage during the specimen preparation process, as a result of the rigid sugar derived cross-links. Closer fibril packing, increased fibril diameters, and irregular diameters have been reported in diabetic tissues, and may result from decades of glycation induced cross-link accumulation.

Animals↗
PubMed1988

Earliest enamel deposits of the rat incisor examined by electron microscopy, electron diffraction, and electron probe microanalysis.

In order to describe initial events in enamel mineralization and to help characterize inorganic-organic interactions in this tissue, the earliest rod and interrod enamel in mandibular incisors from normal young adult (100 gm) rats, perfused with 100% ethylene glycol, has been studied by transmission electron microscopy, selected area electron diffraction, and high-spatial-resolution electron probe microanalysis. Diffraction and probe data were correlated precisely from the same extracellular regions of the tissue. Sites were examined progressively as a function of location a) from the most recently deposited enamel adjacent to ameloblasts toward the dentin-enamel junction and b) from the apical portion of the tooth longitudinally toward its incisal end. Electron diffraction patterns consistent with that of a poorly crystalline hydroxyapatite were generated at all locations. Diffraction characteristics changed only slightly toward that of more crystalline hydroxyapatite at different locations. Earliest apical enamel generated molar Ca/P ratios in a range of 0.99-1.46 (average 1.24 +/- 0.15). Molar Ca/P ratios of the first enamel interrod elements increased from approximately 1.24 at ameloblast-enamel boundaries to approximately 1.40 at the dentin-enamel junction, small changes corresponding to those observed in electron diffraction characteristics.

Animals↗
PubMed1987

Analysis of crystallite shape in rat incisor enamel.

The hydroxyapatite crystallites of mammalian enamel appear as hexagons when seen in cross-sections examined with the transmission electron microscope. Using goniometric transmission electron microscopy, stereo-pair electron micrographs and freeze-fracture replicas, two models have been proposed to explain the hexagonal crystallite profile. The "hexagonal ribbon" model proposes that hexagonal profiles are true cross-sections of elongated hexagonal ribbons. The "rectangular ribbon"model proposes that crystallite profiles are three-dimensional rectangular segments (parallelepipeds), which are contained in the Epon sections and project as opaque hexagons in routine transmission electron micrographs. Morphological observations together with predictions from models indicate that the crystallites in rat incisor enamel are flat ribbons with rectangular cross-sectional profiles. The hexagonal images seen in electron micrographs of thin sections of enamel result from viewing parallelepiped-shaped segments of these crystallites as two-dimensional shadows.

Animals↗
PubMed1986

[Changes in several immunological parameters and the presence of anti-HTLV III antibodies in drug addicts].

The immunological picture in a group of heroin addicts and in a methadone treated group was evaluated. Ninety-six per cent shows modifications of the lymphocyte pattern, independently of the type of opium derivative administered. The OKT4/OKT8 ratio considered one of the hallmarks of acquired immunodeficiency, turns out to be reduced in 64.6% of the cases. In these latter the most outstanding defect is made up by the T-helper drop (83.8% of cases), limited to 23.5% in the group with normal OKT4/OKT8 ratio. The most significant variant between the two groups is represented by the positivity of anti-HTLV III test, which switches from 47 to 74.1% in the patients with reduced ratio. Immunoglobulins turn out to be increased in 81.2% of the cases, independently of the opium derivative administered and without significant differences in relation to the OKT4/OKT8 ratio. Therefore two immunological patterns seem to coexist in the population studied, which very likely represents two evolutive moments of the same disorder with an earlier phase of hyperimmune condition from a persistent antigenic stimulation which characterizes the situation at risk. In a later phase, the impact of HTLV III infection causes the deletion of the lymphocyte helper subpopulation which elicits the immunodepressive situation.

Adolescent↗
PubMed1985

Morphological studies on the distribution of enamel matrix proteins using routine electron microscopy and freeze-fracture replicas in the rat incisor.

Enamel contains two categories of biochemically characterized proteins. Amelogenins are dissociated from enamel without physical disruption of the tissue whereas enamelins are obtained only when the crystallites are dissolved. Ultrastructural visualization of these proteins was attempted using routine electron microscopy and freeze-fracture replicas. Fresh, fixed, and 4.0 M guanidine-HCl-extracted samples of enamel from the secretory (young) and maturation (maturing) stages were compared. Decalcified and stained thin sections of fixed enamel revealed intercrystallite particulate material and "crystallite ghosts" which were identical to the crystallites themselves in young enamel and which corresponded to the periphery of the crystallites in maturing enamel. In contrast, 4.0 M guanidine-extracted enamel contained no intercrystallite particulate material but only "crystallite ghosts." Globular particles observed in freeze-fracture replicas of fresh and fixed enamel samples were also removed by 4.0 M guanidine extraction. Incubation of guanidine-extracted enamel with albumin and ovalbumin solutions restored the globular particles. It was concluded that amelogenins are the nonstructural, heterodispersed particulate material in the intercrystallite space. Enamelins constitute the integral template protein which initially provides for elongation of enamel crystallites. They then regulate the continuous growth in width and thickness during maturation and are progressively displaced to the periphery. The illusion that these "protein ghosts" are contained within the crystallite profile can be explained by the parallelepiped shape of the crystallite segment in thin sections.

Albumins↗
PubMed1983

The effect of osmium postfixation and uranyl and lead staining on the ultrastructure of young enamel in the rat incisor.

Enamel crystallites are electron opaque without osmium or heavy metal staining and give a crystalline electron diffraction pattern. Since the opacity and diffraction pattern are abolished from ultrathin sections of young enamel by floating on distilled water (Bishop and Warshawsky, 1982), the possibility that aqueous staining may also remove crystallites was tested. In addition, the effect of osmium postfixation on crystallite structure was examined. Rat incisors fixed by perfusion with a mixture of aldehydes were either nonosmicated or osmicated prior to dehydration. Incisor segments in the region of inner enamel secretion were embedded in the same Epon block to ensure reliable comparison. Osmicated enamel was more intensely stained with toluidine blue and more electron opaque than nonosmicated enamel. No other structural differences were seen. However, crystallites in osmicated enamel were more resistant to grid demineralization and electron beam damage. Routine staining was done by floating sections on solutions of uranyl acetate and lead citrate; sections were also floated on similar solutions from which the heavy metals were omitted. These solutions removed the electron opaque crystallites from the youngest enamel. Stained sections showed electron opaque crystallite-like structures similar to unstained enamel. When sections that were extracted by the solutions from which the metals were omitted were restained, they appeared identical to routinely stained enamel. It was concluded that staining of young enamel removes the crystallites and reveals only the organic matrix.

Aging↗
PubMed1983

Knife chatter during thin sectioning of rat incisor enamel can cause periodicities resembling cross-striations.

Cross-striations are traditionally associated with the enamel rods in many species including man. Although these striations are obvious with light microscopy, their exact nature has been difficult to determine with the transmission electron microscope on thin sections of enamel. Thin section microscopy either reveals no structures that can be called cross-striations, or shows periodic light and dark bands across the rods. Superficially, these bands resemble chatter artifact. To test this possibility, rat incisor enamel was used because cross-striations have not been demonstrated on these enamel rods. Thin sections were prepared of enamel blocks oriented in various ways with respect to the cutting edge of the diamond knife. The sections showed either uniform enamel or light and dark bands over rod profiles or interrod enamel. Since these bands could be produced artifactually it is concluded that similar bands seen on enamel rods of other species may also be artifacts.

Animals↗