GTP stabilization of adenylate cyclase activated and ADP-ribosylated by choleragen

Choleragen activates adenylate cyclase in human skin fibroblasts by catalyzing the ADP-ribosylation of the 42,000 and 47,000 dalton guanyl nucleotide-binding regulatory components (G) of adenylate cyclase. The ADP-ribose linkage to 42,000 and 47,000 dalton proteins was stable at 30°C for 1 h with or without GTP, whereas GTP was required to stabilize activity of the G proteins. In human erythrocytes, choleragen catalyzed the ADP-ribosylation of only a 42,000 dalton G. The ADP-ribosyl-protein linkage was stable for 1 h at 30°C whether or not GTP was present, despite a rapid loss of G activity in the absence of GTP. Inactivation of choleragen-activated G in both the human fibroblast and human erythrocyte is, therefore, not secondary to the de-ADP-ribosylation of specifically labeled G subunits.     

Influence of growth medium on mineral composition and leaf histology in micropropagated plantlets of Olea europaea

The effects of the medium on the nutritional status and leaf histology of micropropagated shoots have been investigated in two different cultivars of Olea europaea L. The results showed that different media, as well as intraspecific variations between cultivars, strongly influences the mineral composition of the shoots. Furthermore the level of tissue differentiation in vitro was dependent on the medium and appeared to be related to the capacity of plantlets to survive the acclimatation phase. This revised version was published online in June 2006 with corrections to the Cover Date.     

Inhibition of angiogenesis in vitro and in ovo with an inhibitor of cellular protein kinases, MDL 27032.

Protein kinase C (PKC) was implicated as an important positive regulator of angio-genesis by studies showing that tumor promoting phorbol esters, which activate PKC, stimulate angiogenesis both in vitro and in vivo. Therefore, inhibitors of PKC might be expected to block angiogenesis. MDL 27032 [4-propyl-5-(4-pyridinyl)-2(3H)-oxazolone], an inhibitor of cellular protein kinases, prevented capillary-like tube formation by human umbilical vein endothelial cells (HUVEC) on basement membrane preparations, an in vitro model for angiogenic activity. MDL 27032 had an IC50 = 50 microM, whereas MDL 27044, the 4-methyl analog of MDL 27032, was less effective (IC50 greater than 100 microM). This selectivity was reflected in the relative abilities of the two compounds to inhibit PKC and protein kinase A (PKA) activity prepared from HUVEC, and also to inhibit the basic fibroblast growth factor stimulated proliferation of HUVEC. MDL 27032 (0.3 microgram/egg) also significantly inhibited neovascularization in yolk sac membranes of developing chick embryos, whereas MDL 27044 added at concentrations up to 3 micrograms/egg was not inhibitory when compared with vehicle treated controls. Adhesion of HUVEC to individual extracellular matrix proteins, including laminin, fibronectin, and fibrinogen, but not to the mixture of matrix components or collagen type I and IV, was inhibited after treatment with MDL 27032. These studies suggest that MDL 27032, may have potential as an anti-angiogenic agent because it disrupts both formation of tube-like structures by HUVEC on Matrigel and normal neovascularization in ovo. This inhibition may in part be due to altered cellular interactions with the extracellular matrix.     

Magnetic field affects meristem activity and cell differentiation in Zea mays roots

Abstract

Exposure of Zea mays seedlings to a continuous electromagnetic field (EMF) for 30 h induced a 30% stimulation in the rate of root elongation compared with the controls. It also resulted in a significant increase of cell expansion, in both the acropetal (metaxylem cell lineage) and basipetal (root cap cells) direction. In addition, in EMF-exposed roots a precocious structural disorder was observed both in differentiating metaxylem cells and root cap cells. All these features may be consistent with an advanced differentiation of root cells that are programmed to die. EMF treatment also resulted in a significant reduction in the size of the quiescent centre in the root apical meristem. The extent to which these responses are causally linked is discussed.     

Posters

Introduction  Fine needle aspiration (FNA) cytology of the thyroid is a well-established test in the clinical work-up of patients with solitary nodules of the thyroid. Thyroid FNA does however have limitations and audit of diagnostic performance is important.
Methods  The histopathology archives of the Royal Victoria Hospital were searched for all thyroid resections and the histopathological diagnosis was correlated with the pre-operative cytological diagnosis, where available. Special emphasis was placed on the accuracy of tumour diagnosis.
Results  A total of 173 cases were identified during the 2-year period, of these 93 had available pre-operative FNA. A total of 57 tumours were identified. A small number (six of 57) of significant discrepancies were identified. These included a malignant lymphoma diagnosed as Hashimoto's thyroiditis, a metastasis which the FNA had suggested was a medullary carcinoma and an insular carcinoma diagnosed as medullary carcinoma on FNA. False positives included a colloid cyst diagnosed as suspicious of malignancy and a cytological diagnosis of papillary carcinoma not confirmed on histology.
Discussion  At present, the majority of thyroid FNAs in our clinics are performed by surgeons and material is not routinely available for immunocytochemistry. In spite of these limitations, there were few major discrepancies. These might be reduced if pathologist aspirators were able to perform FNAs and collect material for further studies, where necessary. This would allow identification of medullary carcinomas and malignant lymphomas.
Conclusion  FNA of thyroid lesions is a useful investigation in our clinical setting, however, some areas of potential for improvement have been identified.     

Automatic computation of enzyme kinetics by HPLC

Enzyme activity can be easily measured by HPLC using tracesof the product itself as an internal standard. Our procedureinvolved the development of an equation using the experimentaldata obtained in the kinetic assay. The entire procedure canthus be automated and a computer program is presented here forfacilitating the assay and saving time. The determination ofthe activity of NAD kinase is reported as an example. Received on March 15, 1990; accepted on May 17, 1990