PubMed · 8631433
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G J Chiche. 1995. Double-string technique for final impressions--practical applications.. https://pubmed.ncbi.nlm.nih.gov/8631433/
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In invertebrate photoreceptors, illuminated rhodopsin activates multiple G proteins, which are assumed to initiate multiple phototransduction cascades. In this paper, we focused on one of the phototransduction cascades, which utilizes rhodopsin, a Gq-like G protein, and phospholipase C (PLC). A Gq-like G protein from octopus photoreceptors was successfully purified to apparent homogeneity as an active form by simple two-step chromatography. The purified G protein had an alpha beta gamma-trimeric structure consisting of 44-kDa alpha, 37-kDa beta, and 9-kDa gamma subunits. The 44-kDa alpha subunit was assigned to the Gq class by western blot with antiserum against mammalian Gq alpha and by partial amino acid sequencing of its proteolytic fragments. Light-dependent binding of GTP gamma S was observed when the purified octopus Gq was reconstituted with octopus rhodopsin that had been integrated into phospholipid vesicles. Octopus Gq activated PLC beta 1 purified from bovine brain dose-dependently in the presence of A1F4-. Finally, light- and GTP-dependent activation of PLC beta 1 was observed in a reconstitution system consisting of octopus rhodopsin, Gq, and bovine PLC beta 1.
The macrophage mannose receptor specifically recognizes proteins and particles bearing mannose terminal oligosaccharide chains. In the present study, we examined the ability of newly synthesized receptor to bind ligand. Human monocyte-derived macrophages were pulse-labeled with [35S]Met and prepared for affinity chromatography on mannose-Sepharose. Mannose receptor in the flow-through and eluted fractions was detected by fluorography following immunoprecipitation and gel electrophoresis. Labeled mannose receptor was found exclusively in the nonbinding fraction until 10 min of chase. Following a 60-min chase, 67-86% of newly synthesized receptor was precipitated from the bound column fraction. The half-time for development of receptor binding activity was determined to be 35-40 min compared with a 45-min half-time for development of endoglycosidase H resistance. Mannose receptor synthesized by cells incubated in brefeldin A required more than 120 min to acquire endoglycosidase H resistance and maximal binding activity. Inhibitors of N-linked oligosaccharide processing or of O-glycosylation had no effect on the development of mannose receptor binding activity. Monensin prevented terminal sialylation of oligosaccharide side chains but did not inhibit receptor activation. Inclusion of aluminum fluoride in the chase media reversibly inhibited development of endoglycosidase H resistance and mannose-binding activity. We conclude that the mannose receptor undergoes delayed activation following synthesis and suggest that the activating event(s) occur following exit of the receptor from the endoplasmic reticulum and prior to its entry into the trans-Golgi.
Properties of aluminium fluoride (AIF) complex-activated nonselective cation (NS) channels in guinea-pig chromaffin cells were investigated using the patch clamp technique. As the membrane potential was hyperpolarized from the holding potential of -55 mV, the AIF-induced nonselective cation current (INS) diminished progressively. With hyperpolarizations to -100 mV or more negative potentials, the AIF.INS almost instantaneously disappeared. The apparent unit conductance of AIF INS was estimated to be 3 pS by fluctuation analysis. The open state probability of AIF-activated NS channels became large with a decrease in concentration of free Mg2+ ions inside the cell and was less than 0.5 at 12 microM Mg2+. It is concluded that NS channels in the chromaffin cell apparently differ from those in smooth muscle cells.