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At least 505 records · Page 28Linked to original sources
PubMed1990

Invertebrate rhodopsin cleavage by an endogenous calcium activated protease.

Calcium-activated proteases have been purified from a number of vertebrate tissues, including the retina and lens. These proteases exhibit similar characteristics and are believed to be involved in the regulation of cytoskeletal elements. Here we report the partial purification and characterization of a calcium-activated protease from the squid photoreceptor cell which, when activated, specifically removes 10 kDa from the carboxyl-terminal of squid rhodopsin. No other detectable soluble proteins from the invertebrate photoreceptor are susceptible to cleavage and only one non-opsin, integral membrane protein shows evidence of cleavage. The enzyme requires 5 mM calcium for half maximal activation, and is not significantly activated by other divalent ions. The protease has a molecular weight of approximately 350 kDa, as determined by gel filtration, and when partially purified by casein affinity chromatography, it runs as three main bands of 76, 63 and 36 kDa on SDS-PAGE. The crude protease loses as much as 80% of its activity in 24 hr, whereas the partially purified protease is stable up to 4 weeks at 4 degrees C.

Amino Acid Sequence↗
PubMed1992

Light does not induce an increase in cyclic-GMP content of squid or Limulus photoreceptors.

Both slices of squid (Loligo) retinas and Limulus ventral photoreceptors, with or without prior stimulation by flashes of bright light, were rapidly frozen and analysed for cyclic-GMP content by radioimmunoassay. Measurement of the freezing process indicated that freezing occurred at about 100 msec after the light flash. No significant changes in cyclic-GMP content were induced by light in either tissue. These data do not confirm previous reports that cyclic-GMP content of invertebrate photoreceptors is markedly increased by illumination.

Animals↗
PubMed1984

A light-stimulated increase of cyclic GMP in squid photoreceptors.

Photoreceptor outer segments isolated from squid retina are known to contain a light-activated GTP-binding protein. Here it is shown that these photoreceptors contain around 0.01 mol cyclic GMP per mol rhodopsin. Adding GTP in the dark stimulates the production of 0.0003-0.001 mol cyclic GMP/mol rhodopsin per min. GTP and light cause a 2-fold faster increase in cyclic GMP. These results show that either (1) squid rhodopsin activates a guanylate cyclase, or (2) there is a constant guanylate cyclase activity and photoexcited rhodopsin inhibits a cyclic GMP phosphodiesterase.

Animals↗
PubMed1986

Phylogenetic comparison of lens crystallins from the vertebrate and invertebrate--convergent or divergent evolution?

A systematic biochemical comparison has been made of the crystallins isolated from the lenses of five different species belonging to the five major classes of vertebrates. Gel-permeation chromatography of the lens homogenates on Fractogel TSK HW-55(S) revealed well-defined elution patterns with a characteristic distribution of different classes of crystallins from each species. SDS gel electrophoresis and statistical comparison of the amino acid contents indicated that all crystallin groups from different classes share some common subunits and similarity in their amino acid compositions. The results coupled with the relatedness shown in the amino acid compositions of fish gamma-crystallin with those of mammalian gamma-crystallin and the squid crystallin from the invertebrate pointed to the possibility of the existence of a common ancestral protein for all crystallins. This is in favor of the divergent rather than convergent evolution of lens crystallins as commonly assumed in the literature.

Amino Acid Sequence↗
PubMed1988

A novel crystallin from octopus lens.

Lens crystallins were isolated from cephalopods, octopus and squid. Two protein fractions were obtained from the octopus in contrast to only one crystallin from the squid. The native molecular mass for these purified fractions and their polypeptide compositions were determined by gel filtration, sedimentation analysis, and SDS-gel electrophoresis. Octopod and decapod lenses share one common major squid-type crystallin of 29 kDa, with one additional novel crystallin present only in the octopus lens. This newly-characterized crystallin (termed omega-crystallin) exists as a tetrameric protein of 230 kDa, consisting of 4 identical subunits of approx. 59 kDa. It is distinct from the previously known crystallins both in amino acid composition and subunit structure. N-terminal sequence analysis indicated that the omega-crystallin is N-terminally blocked, whereas the major octopus crystallin is identical to the reported squid crystallin with regard to the first 25 residues of protein sequence. Sequence similarity between this major cephalopod crystallin and glutathione S-transferase were found, which suggested some enzymatic role of crystallins inside the cephalopod lens.

Amino Acids↗
PubMed1989

Purification and reconstitution of potassium channel proteins from squid axon membranes.

Voltage-dependent K+ channels are responsible for repolarization of the cell membrane during the late phase of the action potential. Here we report the purification of proteins from squid axon membranes which bind the K+-channel blocker noxiustoxin (NTX), and their subsequent functional reconstitution in planar bilayers. The NTX-affinity purified proteins had Mr values of 60,000 +/- 6,000, 160,000 +/- 15,000 and 220,000 +/- 20,000. Their incorporation into bilayers resulted in single-channel currents with three conductances, the most frequent one of 11 pS in 300/100 mM KCl (cis/trans). The voltage dependence, reversal potential and bursting behavior suggest that these are the K+ channels involved in the squid axon action potential.

Animals↗
PubMed1989

Purification and characterization of Ca2+/calmodulin-dependent actin-binding proteins from squid retina.

Ca2+/calmodulin (CaM)-dependent actin-binding proteins (CABPs) of 92, 105, 120 and 135 kDa were purified from squid retina. These proteins were eluted from the CaM affinity column in a Ca2+-dependent manner, and binding of the CABPs to F-actin was regulated by Ca2+/CaM. Electron microscopic observations employing the low-angle rotary shadowing technique showed the CABP molecules to have granular shapes similar to the granular proteins associated with actin filaments in squid rhabdomeral microvilli. We have previously reported that these actin filaments are fragmented upon exposure to light [(1988) J. Cell Biol. 106, 1151-1160]. Since the intracellular Ca2+ concentrations of the invertebrate retina are elevated during the light illumination, these results indicate that the CABPs are directly associated with the actin filament in the microvilli of the squid photoreceptors. We therefore suggest that the CABPs may regulate the light-induced structural changes of the microvillar cytoskeleton.

Actins↗
PubMed1990

Cloning and nucleotide sequence of cDNA for retinochrome, retinal photoisomerase from the squid retina.

The Rhodopsin-retinochrome system is essential for the visual photoreception of molluscs. cDNA coding for retinochrome of the squid (Todarodes pacificus) was cloned and the nucleotide sequence has been determined. The sequence (2.1 kb) covers the whole coding region of 903 bp. The deduced primary sequence suggests that retinochrome contains seven transmembrane spanning domains. The homology with bovine rhodopsin and the possible retinal binding site are also discussed.

Amino Acid Sequence↗
PubMed1991

Fourier transform infrared spectroscopic study on retinochrome and its primary photoproduct, lumiretinochrome.

Structural studies of retinochrome, and its photoproduct, lumiretinochrome, were done by Fourier transform infrared difference spectroscopy. The absorption bands in the carbonyl stretching region which shift in D2O show the changes in the protein part during the photoreaction. Strong absorption bands in the finger-print region show that the all-trans-retinal chromophore in retinochrome isomerizes to the 11-cis-retinal chromophore in lumiretinochrome upon illumination with yellow-green light at 83K.

Animals↗
PubMed1992

The gamma-subunit of the principal G-protein from squid (Loligo forbesi) photoreceptors contains a novel N-terminal sequence.

The squid (Loligo forbesi) visual system presents as accessible a system for study of G-protein mediated signal transduction as the vertebrate rod outer segment with the added advantage that the major G-protein is a member of the Gq-class. Here the cDNA clone encoding the gamma-subunit of this G-protein is reported, thereby completing the molecular cloning of the heterotrimeric G-protein. The deduced protein structure of G-gamma has relatively little sequence identity with known mammalian counterparts particularly in comparison with the relatively high degree found for both the alpha- and beta-subunits of this protein. In particular, the N-terminus of the squid visual G-gamma contains a repetitive, highly charged region, rich in lysine and glutamate, that has no parallel in other G-proteins. The amino acid sequence of a number of peptides derived by chemical cleavage of G-gamma accounted for much of the protein sequence predicted from the cDNA, including the unusual N-terminal region.

Amino Acid Sequence↗
PubMed1993

Amino acid sequence surrounding the retinal-binding site in retinochrome of the squid, Todarodes pacificus.

Squid (Todarodes pacificus) retinochrome was reduced to N-retinyl protein with borane dimethylamine and cleaved by CNBr. The retinyl peptide was then isolated by chromatography while being monitored for absorbances at 215 and 330 nm, and the N-terminal amino acid sequence was determined to be Ser-Lys-Thr-Gly-X-Ala-Leu-Phe-Pro. This sequence was the same that we had observed at the 7th transmembrane domain of retinochrome whose structure was reported previously. During Edman degradation of the retinyl peptide, the yield of the PTH-lysine at the second cycle was lower than those of the other PTH-amino acids, proving that the lysine residue forms a Schiff's base with retinal (Lys-275 in retinochrome). The amino acid sequence surrounding the retinal-binding lysine in retinochrome greatly differed from those in a variety of known visual pigments. This fact would be associated with the difference in the photoisomerization of chromophore between retinochrome and rhodopsin. The protein structure of retinochrome is also compared with that of rhodopsin in Todarodes.

Amino Acid Sequence↗
PubMed1993

Cephalopod alcohol dehydrogenase: purification and enzymatic characterization.

Octopus, squid and cuttle-fish organs were examined for alcohol dehydrogenase activity. Only one form was detectable, with properties typical of mammalian class III alcohol dehydrogenase. The corresponding protein was purified from octopus and enzymatically characterized. Ion-exchange and affinity chromatography produced a pure protein in excellent yield (73%) after 1600-fold purification. Enzymatic parameters with several substrates were similar to those for the human class III alcohol dehydrogenase, demonstrating a largely conserved function of the enzyme through wide lines of divergence covering vertebrates, cephalopods and bacteria. The results establish the universal occurrence of class III alcohol dehydrogenase and its strictly conserved functional properties in separate living forms. The absence of other alcohol dehydrogenases in cephalopods is compatible with the emergence of the ethanol-active class I type at a later stage, in lineages leading to vertebrates.

Alcohol Dehydrogenase↗