from equine heart, myoglobin (17.6 kDa) from equine heart, pepsin
(35 kDa) from porcine gastric mucosa, bovine serum albumin (BSA, 66.4
kDa), conalbumin (77 kDa) from chicken egg white, concanavalin A (102
kDa) from Canavalia ensiformis, immunoglobulin
G (IgG, ∼150 kDa) from human serum, beta amylase (β-amylase,
223.8 kDa) from sweet potato, chaperonin 60 (GroEL, ∼800 kDa)
from Escherichia coli, ammonium acetate,
tris-acetate, potassium chloride, ethylenediaminetetraacetic acid
(EDTA), adenosine-5′-triphosphate (ATP), magnesium chloride,
ammonium hydroxide, and acetic acid were all purchased from Sigma-Aldrich
(Zwijndrecht, The Netherlands). Methanol, acetone, and LC-MS grade
water were purchased from Biosolve (Valkenswaard, The Netherlands).
Nanospray needles were homemade from preheated borosilicate glass
capillaries (Science Products GmbH, Hofheim, Germany) on a DMZ universal
electrode puller (Zeitz-Instruments Vertriebs GmbH, Munich, Germany)
followed by gold coating with a SC7640 sputter coater (Quorum Technologies,
Kent, UK).