Binding of platelet activating factor to albumin

Binding of platelet activating factor (1-O-alkyl-2-O-acetyl-sn-glycero-3-phosphocholine) to albumin is an important facet of the biological activity of this phospholipid. Measurement of that binding has been hampered by the physical nature of the lipid, which made estimation of the free and bound concentrations difficult. With the use of ultracentrifugation to generate an albumin gradient and to produce a region free of protein, the successful measurement of free PAF and PAF bound to albumin was accomplished. This study has demonstrated that PAF binds to albumin at four binding sites and that the average equilibrium dissociation constant for this binding is 1.10(-7) M. Consideration of these data has led to the hypothesis that the receptor active form of PAF is the albumin-PAF complex, rather than free PAF.     

The effect of periodic habitat fluctuations on a nonlinear insect population model

 Laboratory data show that populations of flour beetles (Tribolium), when grown in a periodically fluctuating volume of flour, can exhibit significant increases in numbers above those attained when grown in a constant volume (of the same average). To analyze and explain this phenomenon a discrete stage-structured model of Tribolium dynamics with periodic environmental forcing is introduced and studied. This model is an appropriately modified version of an experimentally validated model for flour beetle populations growing in a constant volume of flour, in which cannibalism rates are assumed inversely proportional to flour volume. This modeling assumption has been confirmed by laboratory experiments. Theorems implying the existence and stability of periodic solutions of the periodically forced model are proved. The time averages of periodic solutions of the forced model are compared with the equilibrium levels of the unforced model (with the same average flour volume). Parameter constraints are determined for which the average population numbers in the periodic environment are greater than (or less than) the equilibrium population numbers in the associated constant environment. Sample parameter estimates taken from the literature show that these constraints are fulfilled. These theoretical results provide an explanation for the experimentally observed increase in flour beetle numbers as a result of periodically fluctuating flour volumes. More generally, these integrated theoretical and experimental results provide the first convincing example illustrating the possibility of increased population numbers in a periodically fluctuating environment. Received 23 April 1996; received in revised form 28 March 1997     

HuD, a paraneoplastic encephalomyelitis antigen, contains RNA-binding domains and is homologous to Elav and Sex-lethal.

A neuronal antigen (HuD) recognized by the sera of patients with antibody-associated paraneoplastic encephalomyelitis has been isolated by screening a lambda cerebellar expression library. The recombinant antigen provides an unambiguous assay for this rare condition associated with small cell lung cancer. The recombinant antigen has been used to identify specific infiltrating lymphocytes in tumors and affected brain tissues of patients with antibody-associated paraneoplastic encephalomyelitis and sensory neuronopathy. HuD mRNA is uniquely expressed in brain tissue. The HuD protein shows a remarkable homology to the Drosophila proteins Elav and Sex-lethal and is likely to play a role in neuron-specific RNA processing.