Protein Protocols Protein Protocols

616 Bonenfant, Mini, and Jenö
Fig. 3. (A) Amino acid sequence of the K 35–37 peptide obtained by endoproteinase LysC
cleavage of Drosophila melanogaster S6A (corresponding to residues 230–248 of ribosomal
protein S6). The residues labeled with an asterisk indicate the amino acids which become phosphorylated
upon insulin/cycloheximide treatment. (B) Mass spectrum of Ba(OH) 2-treated
RRRSASIRESKSSVSSDKK (K 35–37) from cells stimulated with insulin and cycloheximide.
∆6, ∆5, ∆D4, and ∆3 indicate the number of dehydroalanines arising from Ba(OH) 2 treatment
of K 35–37 carrying 6, 5, 4, and 3 phosphates. The spectrum was obtained by summing up all
scans acquired during the elution of ∆3–∆5 K 35–37 from the capillary reverse-phase column. (C)
Spectrum of Ba(OH) 2-treated K 35–37 from cells that had been treated with okadaic acid prior to
insulin/cycloheximide treatment to suppress phosphatase activity. For labeling of the spectrum,
see (B). (From ref. 18).