. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 12 LI. KOPPELHUS ET Control PP 1 mg/ml AAmix + 3nM PDGF AA mix 3 nM PDGF L-methionine 20 mM KCI 10 20 30 40 50 60 Minutes Figure 4. Effect of different attractants and one repellant. OD of the lower phase was monitored every second minute. PP, protease peptone: AA mix. mixture of amino acids (1 mM of each); PGDF, platelet- derived growth factor. The plots illustrate the chemosensory responses obtained using PP at a concentration of 1 mg mr1 (A), AA mix in combination with 3 nM PDGF (A), AA mix ( + ), 3 nM PDGF ( ), 5 mM
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 12 LI. KOPPELHUS ET Control PP 1 mg/ml AAmix + 3nM PDGF AA mix 3 nM PDGF L-methionine 20 mM KCI 10 20 30 40 50 60 Minutes Figure 4. Effect of different attractants and one repellant. OD of the lower phase was monitored every second minute. PP, protease peptone: AA mix. mixture of amino acids (1 mM of each); PGDF, platelet- derived growth factor. The plots illustrate the chemosensory responses obtained using PP at a concentration of 1 mg mr1 (A), AA mix in combination with 3 nM PDGF (A), AA mix ( + ), 3 nM PDGF ( ), 5 mM L- methionine (O), and 20 mM KCI ($), respectively. OD of the cell suspension used was Cuvettes containing no attractant were tested as controls (D). The data shown represent only some of the data in the experiment. tested in a neutralized HAc-solution seem to indicate that PDGF is itself a very potent chemoattractant to Tetrahymena (Hellung-Larsen et a/., 1986). Insulin induced the maximal response at a concentra- tion of 170 nM. However, \iM insulin had a repellant effect (S/N = ). Such a dramatic change of effect due to a 10-fold rise in concentration has not been observed for any other peptide attractant. All compounds tested were prepared in stock solution just before the experiment (except for the PDGF solution, which had been stored for approximately 1 year at -20°C). Initial screening revealed that /i-endorphin had an atypical loss of activity after only a short storage (2-3 days) in aqueous solution at 0°C. The hormones tested in this experiment were also ex- amined in a capillary assay, and similar results were ob- tained (results not shown). Furthermore, experiments us- ing the capillary method revealed that a-endorphin was also active as an attractant in nanomolar concentrations. We also tested the 17 amino acids present in Holz-defined medium. The amino acids were screened twice at a con- centration of 5 mM. Glutamic acid, glutamine, glycine, iso-
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