Factor V Quebec revisited

Factor V Quebec has been described as a bleeding disorder that exhibits an autosomal dominant inheritance pattern and presents severe bleeding after trauma. Two members of a fourth-generation (IV.13 and IV.15) Canadian family have been studied in detail and are the subject of this report. Their clinical presentations and histories have been described previously (Tracy et al: J Clin Invest 74:1221, 1984). Persistent abnormalities include mild thrombocytopenia and defective platelet factor V. Plasma factor V is present at near normal concentration and is fully functional. Thus, the bleeding diathesis appears to reflect the absence of platelet factor V activity. The recent report (Hayward et al: Blood 84:110a, 1994 [suppl, abstr]) of multimerin deficiency in these individuals led us to reevaluate these patients. Western blot analyses of platelet lysates developed with a variety of monoclonal antibodies show that the alpha-granule proteins, fibrinogen, von Willebrand factor, factor V and osteonectin are decreased in concentration and significantly degraded in the platelets of these patients. Thrombospondin, while not degraded, is substantially decreased. In contrast, platelet factor 4 and beta-thromboglobulin do not appear to be affected. These observations suggest that the alpha- granules are correctly assembled but the contents are subsequently subjected to proteolytic degradation. The results indicate that factor V Quebec disorder is probably associated with a generalized defect that leads to degradation of most proteins of the alpha-granules.     

The relationship of human platelet density to platelet age: platelet population labeling by monoamine oxidase inhibition

The relationship between platelet density and platelet age appears to vary between species with relatively few labeling studies in humans reported. In this study, irreversible monoamine oxidase (MAO) inhibitors were used to biochemically label the circulating platelet population in 15 humans. Platelet samples were then isolated during the 15 days after drug ingestion. The platelets were separated by density on continuous linear Percoll gradients and the density distributions were divided into five fractions containing approximately equal numbers of platelets. Baseline MAO activity was strongly correlated with platelet density. Twenty-four hours after a single dose of tranylcypromine, platelet MAO activities in the density subpopulations were reduced to 14% to 17% of the baseline values. During the first five days after inhibition, the rates of recovery of MAO activity (percentage per day) were inversely proportional to platelet density. The recovery rates in the two most dense fractions were initially slow but increased after five days. Percentage recovery of MAO activity in the least dense fraction was significantly greater than the percentage recovery in the most dense fraction on days 2, 3, 5, and 8 (P less than .01, sign test). These results support the hypothesis that normal human platelets show a small increase in density with age, but they do not exclude the additional possibility that human platelet lifespan is positively correlated with platelet density.     

Modeling of the bryostatins to the phorbol ester pharmacophore on protein kinase C

The bryostatins are macrocyclic lactones that represent an additional structural class of potent activators of protein kinase C. These marine animal biosynthetic products are of unusual interest because they induce only a subset of the biological responses induced by the phorbol esters. We have now determined the binding affinities of naturally occurring and semisynthetic bryostatins for protein kinase C by competition analysis with [26-3H]bryostatin 4 as the radioactive ligand. Esterification of the hydroxyl group at C26 caused dramatic loss of activity as did inversion of the asymmetric center at this position. In contrast, neither of the ester groups at C7 and C20 had a major influence on activity. Computer modeling of the phorbol esters, related diterpenes, and indole alkaloids suggested that the C20, C9, and C4 oxygens of phorbol represented critical elements of the phorbol ester pharmacophore. The C26 oxygen of the bryostatins, together with the C1 and C19 oxygens, gave an excellent spatial correlation with this model, with a root-mean-square deviation of 0.16 A (compared to 0.10-0.35 A among phorbol-related diterpenes). The extension of the phorbol ester pharmacophore model to the bryostatins and its agreement with the structure-activity relations for the bryostatin class of compounds provide additional support for the validity of the model.     

The Role of Autonomy Needs in Suicidal Ideation: Integrating the Interpersonal-Psychological Theory of Suicide and Self-Determination Theory

This study investigated the role of autonomy satisfaction in the development of suicidal ideation by integrating two theoretical models of suicide-related behaviors. The first hypothesized a direct effect of autonomy on suicidal ideation. The second hypothesized an indirect effect of autonomy on suicidal ideation via perceived burdensomeness and thwarted belongingness. This was a cross-sectional study of 449 college students, who were predominantly female (73.1%) and Hispanic (70.6%), with a mean age of 20.40 years (SD = 4.38, range 18–50 years). Participants were recruited from a psychology participant pool and completed self-report survey measures for course credit. The model of indirect effects provided the best fit to the data; relatedness, autonomy, and competence were significantly associated with higher thwarted belongingness and perceived burdensomeness, which, in turn, were significantly associated with higher suicidal ideation. Future studies should test this model longitudinally and consider autonomy as a possible avenue for the prevention of suicide-related behaviors.     

Purification and characterization of branched chain α-keto acid dehydrogenase complex of bovine kidney

A branched chain alpha-keto acid dehydrogenase-dihydrolipoyl transacylase complex was purified to apparent homogeneity from bovine kidney mitochondria. As usually isolated, the complex (s(20,w) = 40 S) contained little, if any, dihydrolipoyl dehydrogenase. When saturated with the latter enzyme the complex had a specific activity of about 12 mumol of alpha-ketoisovalerate oxidized per min per mg of protein at 30 degrees with NAD(+) as electron acceptor. In addition to alpha-ketoisovalerate, the complex also oxidized alpha-ketoisocaproate, alpha-keto-beta-methylvalerate, alpha-ketobutyrate, and pyruvate. The ratios of the specific activities were 2.0:1.5:1.0:1.0:0.4, and the apparent K(m) values were 40, 50, 37, 56, and 1000 muM. The complex was separated into its component enzymes. The branched chain alpha-keto acid dehydrogenase (6 S) consists of two different subunits with estimated molecular weights of 46,000 and 35,000. The dihydrolipoyl transacylase (20 S) contains apparently identical subunits of molecular weight about 52,000. In the electron microscope, the transacylase has the appearance of a cube, and the molecules of branched chain alpha-keto acid dehydrogenase appear to be distributed on the surface of the cube. In contrast to the pyruvate dehydrogenase complex of bovine kidney, the branched chain alpha-keto acid dehydrogenase complex apparently is not regulated by phosphorylation-dephosphorylation. Its activity, however, is subject to modulation by end-product inhibition.