Hexokinase 2 from Saccharomyces cerevisiae: regulation of oligomeric structure by in vivo phosphorylation at serine-14

Homodimeric hexokinase 2 from Saccharomyces cerevisiae is known to have two sites of phosphorylation: for serine-14 the modification in vivo increases with glucose exhaustion [Kriegel et al. (1994) Biochemistry 33, 148-152], while for serine-157 it occurs in vitro with ATP in the presence of nonphosphorylateable five-carbon analogues of glucose [Heidrich et al. (1997) Biochemistry 36, 1960-1964]. We show now by site-directed mutagenesis and sedimentation analysis that serine-14 phosphorylation affects the oligomeric state of hexokinase, its substitution by glutamate causing complete dissociation; glutamate exchange for serine-157 does not. Phosphorylation of wild-type hexokinase at serine-14 likewise causes dissociation in vitro. In view of the higher glucose affinity of monomeric hexokinase and the high hexokinase concentration in yeast [Womack, F., and Colowick, S. P. (1978) Arch. Biochem. Biophys. 191, 742-747; Mayes, E. L., Hoggett, J. G., and Kellett, G. L. (1983) Eur. J. Biochem. 133, 127-134], we speculate that the in vivo phosphorylation at serine-14 as transiently occurring in glucose derepression might provide a mechanism to improve glucose utilization from low level and/or that nuclear localization of the monomer might be involved in the signal transduction whereby glucose causes catabolite repression.     

Critical pharmacologic management in the emergency department

PURPOSE: Starting from a status hypercoagulability previous to substitutive hip and knee surgery, the aim of this work was to investigate the influence of different osteoarthropatic pictures for which arthroplasty is indicated in the activation of the clotting cascade, rheumatoid arthritis (RA) being one of such pictures. PATIENTS AND METHODS: Of 79 patients suitable for prosthetic surgery of hip (53) and knee (26), the preoperative values of several markers, namely, D dimers (D-D), thrombin-antithrombin (TAT) complex, and F1 + 2 prothrombin fragment (F1 + F2) were assessed by enzymoimmunoasay. The mean age of the patients was 65.5 years, and their sex distribution was 50 women and 29 men. The indications for arthroplasty were as follows: osteoarthrosis (62), aseptic necrosis (11), RA (9), articular gout (2), previous fracture (2), more than one diagnosis overlapped in some cases. The results attained were compared with a control group comprised of 33 subjects (16 women and 17 men) with mean age similar to the patient's group (68.06 years). RESULTS: The D-D values in the patients suitable for hip arthroplasty and the TAT values in patients suitable for both types of surgery were significantly higher than those found in the control group (p = 0.012 and 0.01, respectively). The preoperative TAT levels of the RA patients were significantly higher (p = 0.025) than those found in the patients with the other surgical indications. CONCLUSIONS: Previously to the performance of arthroplasty, the patients show hypercoagulative marker values higher than those of age-matched controls. The significant rising of TAT found in RA patients is concordant with the literature, and this fact makes it advisable to include RA among the pathologic situations associated with hypercoagulability, as this is a common indication for substitutive hip and knee surgery with high risk of venous thromboembolic disease.     

Interkinetic nuclear migration in nasal placode of chick embryo

Cells of nasal placode of chick embryos were studied with thymidine H3 and autoradiography. Our results shown, that the nuclei in the nasal placode synthesize DNA in the outer zone, then migrate toward the inner zone to undergo division and subsequently return to the outer zone.     

Sustaining the structure of the professional self

We describe a patient with an intrahepatic biliary hamartoma associated with transformation to undifferentiated carcinoma which responded to intrahepatic arterial floxuridine chemotherapy.     

Pleomorphic xanthoastrocytoma: DNA flow cytometry and outcome analysis of 12 patients

BACKGROUND: Pleomorphic xanthoastrocytoma (PXA) is an astrocytic tumor occurring primarily in childhood and adolescence with some malignant histologic features but a relatively slow clinical course. However, some tumors progress more rapidly and can undergo malignant degeneration. The authors attempted to determine whether various histologic features or tumor cell proliferative indices might help identify lesions at risk for early progression and distinguish PXAs from malignant gliomas. METHODS: In a retrospective study of 12 patients with PXA, the tumor's histologic features and DNA flow cytometric parameters were compared with their clinical course. DNA flow cytometry values for the S- and G2-phase of the PXAs also were compared with control group samples of malignant and low grade astrocytomas. RESULTS: Of the 12 tumors at initial diagnosis, 5 were considered typical PXAs whereas 7 had some atypical features (4 with paucity of reticulin fibers, 1 with focal necrosis, and 2 with both atypical reticulin and focal necrosis). During the follow-up period (range, 3.75-11 years; mean, 6.8 years), 2 patients had recurrences; 1 atypical reticulin PXA progressed to glioblastoma after 6.5 years and the 1 tumor with focal necrosis recurred at 6 months and again at 2 years with typical histologic features. DNA flow cytometry parameters of the typical PXA group were similar to values for malignant astrocytoma and significantly higher than values for control specimens of low grade astrocytomas. There were no distinctive DNA flow cytometric features that could distinguish this last tumor from others with a more benign clinical course. CONCLUSIONS: Measurements of the S-phase and G2-phase obtained from DNA flow cytometry and atypical histologic features cannot reliably identify PXA patients at risk for early progression and overall are significantly higher than values obtained for low grade gliomas. Therefore, frequent (i.e., two to three times per year) postoperative clinical and radiologic examinations are necessary to judge the appropriateness of adjuvant therapy in patients with PXA. The paradox of slow growth but DNA flow cytometry consistent with aggressive malignant lesions may represent a cell-cycle arrest mechanism in these lesions that could be verified in subsequent studies.