Fifth, we found that eliminating acetic acid from the extraction solvent resulted in enhanced levels of the Orc[1-11] peptide, while Orc[1-11]-OMe was no longer detected. This supported work showing that enzymatic methanolysis is favored over hydrolysis for enzymes functioning under more acidic pH conditions . Finally, we also demonstrated that, under conditions where the pH is reduced, methanol can act as a competing nucleophile to yield a C-terminally Selleck AG-14699 methylated product using the serine protease, trypsin. Because previously reported Orc[Ala11] is isobaric with the extraction artifact, Orc[1-11]-OMe, we attempted to determine if
low abundance levels of Orc[Ala11] were obscured and undetected in our analyses with methanol. To address these concerns, we carried out three independent extraction-based analyses of eyestalk tissues, namely, (1) MALDI-FTMS analyses of eyestalk ganglion extracts using non-methanolic solvent systems (acidified acetone and saturated DHB), (2) HPLC Chip–nanoESI Q-TOF MS analyses of pooled eyestalk extracts, all heat-treated
to deactivate enzymes and extracted using a solvent composition that was used in previous studies, and (3) MALDI-FTMS of sinus gland tissues extracted with full methyl esterification, which provides an additional way to distinguish Orc[Ala11] and Orc[1-11]-OMe. These three independent approaches failed to show any evidence to support INCB024360 ic50 the presence of Orc[Ala11] as a peptide endogenous to the lobster. To determine if we were able to detect Orc[Ala11] by direct tissue analyses, we analyzed additional eyestalk tissues and other H. americanus neuronal glands and tissues (PO, brain, STG, and CoG) by direct tissue MALDI-FTMS, where methanol is not used in any steps of our tissue preparation protocol. All of our measurements, which often included multiple sub-samples
dissected from larger tissues (PO and brain), and which represented measurement from a minimum of three individuals and a maximum of greater than 20 individuals for SG and CoG samples, failed to show any evidence of peaks characteristic of Orc[Ala11] in any spectra. While Smoothened it is impossible to prove that a peptide is not present in an organism, our best efforts, using direct tissue analyses and three independent extraction-based approaches, failed to show signals supporting prior work identifying Orc[Ala11] as a peptide endogenous to the lobster. Acidified methanol has been used as the extraction solvent of choice in many previous investigations of invertebrate neuropeptides , , , ,  and . For the extraction of crustacean tissues, research groups have commonly used methanolic solvent systems composed of 90% methanol, 1% water , ,  and  or 9% water , and acetic acid.