SDS/PAGE separation of EGTA-extracted gastrolith proteins
revealed the presence of at least six distinct prominent proteins
(Fig. 1A), with an 65-kDa species, termed GAP 65 (gastrolith
protein 65) being most abundant. GAP 65-enriched HPLC
fractions were separated by SDS/PAGE and detected with
Coomassie brilliant blue, ‘‘stains all’’ (for negatively charged
proteins), or periodic acid-Schiff’s reagent (PAS) (for glycoproteins)
(Fig. 1B), showing that GAP 65 is a negatively charged
glycoprotein.