Erythrocyte isozymes of phosphofructokinase in genetically high- and low-2,3-diphosphoglycerate rats

A major locus (Dpg) with two alleles (d and D) controls erythrocyte 2,3-diphosphoglycerate (DPG) levels in Long-Evans rats and is closely linked to a locus (Hbb) determining a hemoglobin electrophoretic polymorphism. Glycolytic intermediate levels and phosphofructokinase (PFK) kinetic studies suggest that in vivo PFK activity differences underlie the differences in DPG levels. We report here chromatographic and immunologic evidence that rat erythrocyte PFK is composed of two isozymes which elute from DEAE-Sephadex at positions identical to those of the isozymes in platelets and liver, respectively. The percentage of platelet-type PFK is significantly (P less than 0.05) smaller in low-DPG (dd) hemolysates than in DD hemolysates regardless of hemoglobin phenotype. When hemolysates were prepared in a stabilizing buffer, PFK specific activity was significantly (P less than 0.005) higher in DD rats. These data suggest that the PFK kinetic differences may result from alterations in the isozyme composition of active PFK.     

Changing trends in gynaecological surgical workload.

A reduction has been recorded in National Health Service gynaecological bed occupancy in Winchester and Wessex. At least part of this change may be explained by an increase in private hospital practice. NHS managers should plan for similar changes elsewhere in the United Kingdom.     

Spectroscopic studies of protein-heme interactions accompanying the allosteric transition in methemoglobins

Resonance Raman, optical absorption, and circular dichroism spectroscopic techniques have been used to examine the effect of the addition of inositol hexaphosphate (IHP) to a series of carp and human methemoglobin derivatives. Markers of spin equilibrium in the high-frequency region (1450-1650 cm-1) of the resonance Raman spectrum yield high/low-spin ratios consistent with direct magnetic susceptibility measurements. Changes in the low-frequency region (100-600 cm-1) of the resonance Raman spectrum appear to correlate with the quaternary structure transition. Changes in the ultraviolet absorption spectra and the circular dichroism spectra also appear to be related to the quaternary structure change. By using the resonance Raman spin markers, we find that those derivatives of carp methemoglobin which are in spin equilibrium have a larger ratio of high-spin to low-spin populations than the corresponding derivatives of human methemoglobin. Upon the addition of IHP to the methemoglobins the spin equilibrium is shifted toward a larger high-spin population. This change in equilibrium is larger for the carp protein than for the human protein. We obtain an IHP-induced change in the free energy difference between the high-spin and low-spin states of 300 cal/mol for those human methemoglobins in which a quaternary structure change occurs and 600 cal/mol for carp methemoglobins. Our data are consistent with a quaternary structure change induced by IHP in all the carp methemoglobins studied (F-, H2O, SCN-, NO2-, N3-, and CN-) and in the F-, H2O, and SCN- derivatives of the human protein but not in the NO2-, N3-, and CN- derivatives. The Fe-CN stretching mode has been identified by isotopic substitution and found to be unchanged in frequency in carp CN- metHb when the quaternary structure is changed. On the basis of our results we conclude that the protein forces at the heme due to the addition of IHP do not significantly affect the position of the iron atom with respect to the heme plane. Rather, the changes in spin equilibrium may be caused by protein-induced changes in the orientation of the proximal histidine or tertiary structure changes in the heme pocket which affect the porphyrin macrocycle. Either of these changes, or a combination thereof, leads to changes in the iron d orbital energies and concomitant changes in the spin equilibrium.     

The role of expert systems in vegetation science

An area of artificial intelligence known as experts systems (or knowledge-based systems) is being applied in many areas of science, technology and commerce. It is likely that the techniques will have an impact on vegetation science and ecology in general. This paper discusses some of those impacts and concludes that the main effects will be in areas of applied ecology especially where ecological expertise is needed either quickly (e.g. disaster management) or across a wide range of ecological disciplines (e.g. land management decisions). Expert systems will provide ecologists with valuable tools for managing data and interacting with other fields of expertise. The impact of expert systems on ecological theory will depend on the degree to which deep knowledge (i.e. knowledge based on first principles rather than on more empirical rules) is used in formulating knowledge bases.     

Escherichia coli heat-labile enterotoxin. Nucleotide sequence of the A subunit gene

We report the complete DNA sequence of the Escherichia coli elt A gene, which codes for the A subunit of the heat-labile enterotoxin, LT. The amino acid sequence of the LT A subunit has been deduced from the DNA sequence of elt A. The LT A subunit starts with methionine, ends with leucine, and comprises 254 amino acids. The computed molecular weight of LT A is 29,673. The A subunit of cholera toxin (CT A) has been shown to be structurally and functionally related to the LT A subunit. Comparison of the primary structure of LT A with the known partial amino acid sequence of CT A indicates that the 2 polypeptides share considerable homology throughout their sequences. The NH2-terminal regions exhibit the highest degree of homology (91%), while the COOH-terminal region, containing the sole cystine residue in each toxin is less conserved (approximately 52%). Alignment of homologous residues in the COOH-terminal regions of LT A and CT A indicates that a likely site for proteolytic cleavage of LT A is after Arg residue 188. The resulting A2 polypeptide would be 46 amino acids long, would contain a single cysteine residue, and have Mr = 5261. The elt A nucleotide sequence further predicts that the LT A protein is synthesized in a precursor form, possessing an 18-amino acid signal sequence at its NH2 terminus.