Functional characterization of leucine transport induced in Xenopus laevis oocytes injected with mRNA isolated from midguts of lepidopteran larvae (Philosamia cynthia).
The injection of poly(A)+ mRNA prepared from Philosamia cynthia midgut caused time- and dose-dependent increases of leucine transport in Xenopus laevis oocytes, with an increase in leucine uptake 1.5-3 times that of oocytes injected with water. When the NaCl concentration was reduced from 100 to 5 mmol l-1, the difference between mRNA- and water-injected oocytes was greater and a fourfold increase of L-leucine uptake was measured. D-Leucine (10 mmol l-1) completely inhibited the induced uptake of 0.1 mmol l-1 L-leucine. The newly expressed component of L-leucine uptake increased at alkaline pH and was abolished by incubation for 15 min with 15 mmol l-1 phenylglyoxal. The mean Km values, calculated using Na+ activation curves of leucine uptake, were 23.3 +/- 6.1 mmol l-1 in water-injected oocytes and 0.4 +/- 0.2 mmol l-1 for the newly expressed component of leucine uptake in mRNA-injected oocytes. On the basis of these results, we conclude that the increase of L-leucine uptake in mRNA-injected oocytes was due to the expression of a new transport system, which differs from the endogenous ones and shares many features with that found previously in Philosamia cynthia midgut.
Sacchi
V F
VF
Istituto di Fisiologia Generale e di Chimica Biologica, Facoltà di Farmacia, Milano, Italy.
Perego
C
C
Magagnin
S
S
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D005260:Female; D006863:Hydrogen-Ion Concentration; D007267:Injections; D007814:Larva / Q000737:chemistry; D007915:Lepidoptera / Q000737:chemistry*; D007930:Leucine / Q000378:metabolism*; D008871:Microvilli / Q000737:chemistry*; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism*; D012333:RNA, Messenger / Q000302:isolation & purification / Q000494:pharmacology*; D012964:Sodium / Q000378:metabolism; D014982:Xenopus laevis / Q000378:metabolism*
D012333:RNA, Messenger; D012964:Sodium; D007930:Leucine