"Shear induced platelet activation"--a critical reappraisal

Platelets were found to be stimulated by high shear exposure for 5 minutes. Using a new technique, shear stresses up to 255 N/m2, acting for pathophysiological relevant intervals of milliseconds did not elicit active release of beta-TG, beyond the amount explained by LDH-monitored passive lysis. Neither the plasma level of ionized calcium (citrate vs heparin anticoagulation), nor a potent platelet inhibiting agent like PgI2 (20 nM) did significantly alter platelet responses to short acting high shear stress. Ultrastructural signs of activation could largely be suppressed by adding ADP-scavengers. Direct "shear induced platelet activation" appears rather unlikely and mostly reducible to secondary biochemical activation by mediators, probably adenine nucleotides, from a small percentage of passively shear-destroyed platelets. The extent of this secondary activation is largely a matter of experimental conditions.     

Cloning of hexokinase structural genes from Saccharomyces cerevisiae mutants with regulatory mutations responsible for glucose repression.

The regulatory hexokinase PII mutants isolated previously (K.-D. Entian and K.-U. Fröhlich, J. Bacteriol. 158:29-35, 1984) were characterized further. These mutants were defective in glucose repression. The mutation was thought to be in the hexokinase PII structural gene, but it did not affect the catalytic activity of the enzyme. Hence, a regulatory domain for glucose repression was postulated. For further understanding of this regulatory system, the mutationally altered hexokinase PII proteins were isolated from five mutants obtained independently and characterized by their catalytic constants and bisubstrate kinetics. None of these characteristics differed from those of the wild type, so the catalytic center of the mutant enzymes remained unchanged. The only noticeable difference observed was that the in vivo modified form of hexokinase PII, PIIM, which has been described recently (K.-D. Entian and E. Kopetzki, Eur. J. Biochem. 146:657-662, 1985), was absent from one of these mutants. It is possible that the PIIM modification is directly connected with the triggering of glucose repression. To establish with certainty that the mutation is located in the hexokinase PII structural gene, the genes of these mutants were isolated after transforming a hexokinaseless mutant strain and selecting for concomitant complementation of the nuclear function. Unlike hexokinase PII wild-type transformants, glucose repression was not restored in the hexokinase PII mutant transformants. In addition mating experiments with these transformants followed by tetrad analysis of sporulated diploids gave clear evidence of allelism to the hexokinase PII structural gene.     

Cytology of extrapulmonary Pneumocystis carinii infection in the acquired immunodeficiency syndrome.

Rare cases of extrapulmonary Pneumocystis carinii (EPPC) have been seen in patients with acquired immunodeficiency syndrome (AIDS). We report seven such diagnoses of nonpulmonary P carinii (PC) from four AIDS patients between 1986 and 1989. The specimens included fine needle aspirate of liver, spleen, periarticular tissue and pleura as well as ankle fluid, pleural fluid and ascites. In some, but not all, cases the patients had concurrent or previous episodes of PC pneumonia. In all cases the typical granular, eosinophilic aggregates of PC cysts were noted on routine Papanicolaou staining, leading to the definitive detection of PC cysts with Grocott silver stain. In most cases, evidence for granulomalike and neovascularized tissue reaction was present in cytologic material. One specimen demonstrated concurrent acid fast bacilli. In the setting of AIDS, cytology of effusions and masses should include an evaluation for EPPC.     

Allosteric inhibition by phosphoenolpyruvate of glucose-6-phosphate dehydrogenase from bacteria and its taxonomic importance

Purified glucose-6-phosphate dehydrogenase from Zymomonas mobilis was examined with respect to inhibition by phosphoenolpyruvate, ADP and ATP. Its molecular weight was 260,000 and the kinetics of substrate conversion indicated a random bi bi mechanism. This enzyme and the dehydrogenases from Z. anaerobia, Azotobacter chroococcum, A. vinelandii, and “Corynebacterium” autotrophicum strain 19/-/x were found to be allosterically inhibited by phosphoenolpyruvate, while those from several coryneform bacteria and from Escherichia coli or Pseudomonas fluorescens were not.