No abstract

The effects of temperature on protein synthesis by Escherichia coli, a mesophile, and Pseudomonas fluorescens, a psychrotroph, were investigated by using whole-cell and cell extract preparations. After shifts to 5°C, protein was synthesized at a slowly decreasing rate for 1 h by both organisms, after which P. fluorescens synthesized protein at a new rate corresponding to its 5°C growth rate, in contrast to E. coli which did not synthesize protein at a measurable rate. In vitro protein-synthesizing systems using MS-2 RNA, endogenous mRNA, and purified polysomes were utilized to investigate initiation of translation at 5°C. In these systems, P. fluorescens cell extracts synthesized protein at linear rates for up to 2 h at 50C, whereas E. coli cell extracts synthesized protein for only 25 min

We have used a 20 liter stirred tank fermentor, equipped with a 127 mesh ethylene-tetrafluoroethylene rotating screen for cell recycle, for the continuous production of recombinant single chain urokinase-type plasminogen activator (rscu-PA) from Chinese hamster ovary (CHO) cells. Viable cell densities between 60 and 74 million per ml were maintained at medium perfusion rates of 3.0 to 4.0 fermentor volumes per day. Cells were retained by the 120 micron nominal opening filter through the formation of "clumped" cell aggregates of 200 to 600 microns in size, which did not foul the filter. In 31 days of culture, a total of 51 grams of rscu-PA were produced in 1,000 liters of medium. The rscu-PA produced over the course of this continuous culture was purified and characterized both in vitro and in vivo and shown to be comparable to natural scu-PA produced from the transformed human kidney cell line, TCL-598.

Two plasmin-resistant mutant forms of pro-urokinase (pro-UK) constructed by site-directed mutagenesis of Lys'58 to Val'5 and Met'58 were used to evaluate the intrinsic enzymatic and fibrinolytic properties of pro-UK as distinct from those of its two-chain UK (TC-UK) derivative. Both mutants, while resistant to plasmin activation, were as sensitive as pro-UK to degradation by thrombin. Since thrombin cleaves a peptide bond only two residues from the activation site, the integrity of this loop was maintained in the two mutants. The amidolytic and plasminogen-activating activities of the mutants averaged 0.14 and 0.12% that of TC-UK, respectively. The fibrin plate activities were 2,400 JU/ml and 700 1U/mg for the Met'58 and Val"5 mutants or about 1.5% that of TC-UK. These findings attest to a discrete but low intrinsic activity for pro-UK and suggest that the higher values reported in the literature may be related to UK contaminants or plasmin-induced TC-UK generation during the assay. Clot lysis by the mutants required doses > 100-fold higher than those of pro-UK to induce a comparable effect. From this it appears that pro-UK activation is a major determinant of the rate of clot lysis occurring with pro-UK. Clot lysis by the mutants was potentiated by plasmin pretreatment of the fibrin and by the addition of small amounts of TC-UK or tissue plasminogen activator (t-PA). Combinations of t-PA and the mutants were synergistic in their fibrinolytic effects. These findings mirror those previously obtained with pro-UK. We concluded that the previously described potentiation of pro-UK-induced clot lysis by UK or t-PA is mediated primarily by pro-UK itself rather than by a promotion of its activation.

Mouse interferons of three size classes (A, 35,000 to 40,000 daltons; B, 26,000 to 33,000 daltons; and C, 20,000 daltons) were purified from Ehrlich ascites tumor cells infected with Newcastle disease virus. The sequences of the first 24 amino acids (No. 17 has not been identified) of interferons A and B are identical. The sequence of the first 20 amino acids of interferon C differs from that of A and B in 18 positions. There is partial homology in amino terminal sequence between mouse interferons A (or B) and a human fibroblast interferon and between mouse interferon C and a human lymphoblastoid interferon.