Isolation of a calcium-binding phosphoprotein from the oocytes and hemolymph of the blood-sucking insect Rhodnius prolixus.
A novel calcium-binding phosphoprotein was isolated from the oocytes of the blood-sucking bug Rhodnius prolixus. This protein exhibits an apparent molecular mass of 18 kDa on gel filtration, but migrates as an 8-kDa band on N-[2-hydroxy-1,1-bis(hydroxymethyl)ethyl]glycine/SDS-polyacrylamide gels. It has a high content of serine (24% of the total number of residues), and phosphoserine is the sole amino acid phosphorylated in vivo. A similar protein was partially purified from the hemolymph. It resembles the oocyte form of the protein in its NH2-terminal sequence and its ability to be taken up by growing ovaries. 45Ca binding to the oocyte phosphoprotein was determined after SDS-polyacrylamide gel electrophoresis followed by blotting on nitrocellulose membranes. Titration of Ca2+-binding sites shows a high capacity (approximately 50 mol/mol of protein), but a low affinity (K0.5 congruent with 10(-3) M). Based on these characteristics, we have named this protein Rhodnius calcium-binding phosphoprotein. It resembles phosvitin, a phosphoprotein present in the oocytes of nonmammalian vertebrates.
Silva-Neto
M A
MA
Departamento de Bioquímica Médica, Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro, P. O. Box 68041, Rio de Janeiro CEP 21941-590, RJ, Brasil. maneto@server.bioqmed.ufrj.br
Atella
G C
GC
Fialho
E
E
Paes
M C
MC
Zingali
R B
RB
Petretski
J H
JH
Alves
E W
EW
Masuda
H
H
D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D006458:Hemolymph / Q000378:metabolism*; D008969:Molecular Sequence Data; D009865:Oocytes / Q000378:metabolism*; D010053:Ovary / Q000378:metabolism; D010750:Phosphoproteins / Q000737:chemistry / Q000302:isolation & purification* / Q000378:metabolism; D010761:Phosphorus Radioisotopes; D011485:Protein Binding; D012239:Rhodnius / Q000378:metabolism*
D010750:Phosphoproteins; D010761:Phosphorus Radioisotopes; D002118:Calcium