Application of mobilities in electromagnetic fields to the determination of kinetic parameters

Changes in electrophoretic and/or electromagnetophoretic mobilities during the course of biochemical reactions are related to first order rate constants of those reactions. By linearization of the mobility/reaction-coordinate relations, a method for the determination of rate constants is suggested, an assessment being made of some likely advantages and limitations of this approach to kinetic problems.     

Tryptophan Biosynthesis in Cell Cultures of Nicotiana tabacum

Some of the general features of the pathway for l-tryptophan biosynthesis in cell cultures of Nicotiana tabccum var. Wisc. 38 have been investigated. The results of both isotope competition and direct-labeling experiments show that shikimic acid, anthranilic acid, indoleglycerol phosphate, and indole can serve as precursors to l-tryptophan in these cells, indicating that, in terms of its biochemical intermediates, the pathway is similar to that described for the bacteria and fungi.     

Protein Synthesis in Sonically Damaged Escherichia coli

By gentle sonic treatment, Escherichia coli cells were modified to permit penetration of actinomycin D, adenosine triphosphate, trypsin, ribonuclease, and polyuridylic acid. The behavior of these "soniplasts" as protein-synthesizing particles was investigated.     

Etude de la Faune submicroscopique de quelques tourbières à sphagnum

Sans résumé     

1-Methyladenine in urine of an adenosine deaminase-deficient adult without immunodeficiency

Procedures are described for the isolation and identification of 1-methyladenine from the urine of an adult female with adenosine deaminase deficiency but no immunodeficiency. Evidence is provided indicating that much of the usual urinary excretion product, 1-methyladenosine, is converted to 1-methyladenine in this subject prior to excretion. Since the nucleoside phosphorylases present in normal individuals do not act on 1-methyladenosine, this suggests that a phosphorylase with unusual properties is present in this adenosine deaminase-deficient subject. A possible role for this phosphorylase in removal of deoxyadenosine in this subject is discussed.     

Tyrosine phosphorylation is an obligatory event in IL-2 secretion.

Activation of T lymphocytes leads to the production of the T cell growth factor IL-2 that regulates T cell proliferation. This activation is associated with several potential intracellular signalling events including increased activity of phospholipase C (PLC) and resultant increases in production of inositol phosphates and diacylglycerols. In addition, phosphorylation of specific intracellular proteins on serine, threonine, and tyrosine residues increases. The role of each of these events in IL-2 production is unclear. Using Western blotting with antiphosphotyrosine antibodies, we demonstrate that activation of murine T cells with mitogenic lectins or anti-CD3 antibodies leads to a rapid increase in tyrosine phosphorylation of proteins of 120, 72, 62, 55, and 40 kDa. Similar patterns of antiphosphotyrosine antibodies reactivity were observed in splenocytes, a T cell hybridoma, and a T lymphoma. Tyrosine phosphorylation was detectable within minutes of addition of mitogenic lectins and persisted for at least 6 h. Pretreatment of the cells with pertussis toxin did not inhibit tyrosine phosphorylation indicating that a pertussis toxin-sensitive G protein is not involved in signal transduction. Neither increasing cytosolic-free calcium nor activating protein kinase C mimicked the effects of mitogenic lectins suggesting that tyrosine phosphorylation was not a consequence of activation of PLC. This was confirmed by demonstrating that mitogenic lectins induced similar patterns of tyrosine phosphorylation in cells in which activation of the TCR leads to increased PLC activity and in cells in which PLC is not stimulated. To test whether tyrosine phosphorylation is linked to IL-2 secretion, we determined the effect of three specific tyrosine kinase inhibitors (tyrphostins) on tyrosine phosphorylation, IL-2 secretion, and cellular proliferation. The concentration dependence of inhibition of tyrosine phosphorylation and IL-2 production were similar. However, higher concentrations of the tyrphostins were required to inhibit constitutive proliferation of the T cell line indicating that inhibition of IL-2 secretion was not secondary to nonspecific toxic effects of the tyrphostins. Addition of the tyrphostins after mitogenic lectin decreased the amount of tyrosine phosphorylation and IL-2 secretion in parallel. This indicates that both tyrosine kinases and phosphatases are activated and that continuous tyrosine phosphorylation is likely required for IL-2 secretion. Therefore, tyrosine phosphorylation appears to represent an obligatory event in the transmembrane signaling processes that lead to IL-2 secretion.