Catalyzes ghrelin acylation at 'Ser-3' using preferentially octanoyl-CoA, hexanoyl-CoA and decanoyl-CoA as acyl-CoA donors leading to ghrelin activity (PubMed:18267071, PubMed:24045953, PubMed:28134508, PubMed:18669668, PubMed:18443287, PubMed:19501572). In vitro uses also acyl-CoA donors of different lengths from short-chain (C2) to long-chain fatty acids (C16) knowing that acyl-CoA donors from butanoyl-CoA (C4) to dodecanoyl-CoA (C12) are more efficient compared to longer acyl-CoA donors, such as myristoyl-CoA (C14) and palmitoyl-CoA (C16) that are not efficient (PubMed:19501572). Inactive octanoyltransferase activity. L-seryl-[protein] + octanoyl-CoA = CoA + O-octanoyl-L-seryl-[protein] hexanoyl-CoA + L-seryl-[protein] = CoA + O-hexanoyl-L-seryl-[protein] decanoyl-CoA + L-seryl-[protein] = CoA + O-decanoyl-L-seryl-[protein] acetyl-CoA + L-seryl-[protein] = CoA + O-acetyl-L-seryl-[protein] butanoyl-CoA + L-seryl-[protein] = CoA + O-butanoyl-L-seryl-[protein] L-seryl-[protein] + pentanoyl-CoA = CoA + O-pentanoyl-L-seryl-[protein] heptanoyl-CoA + L-seryl-[protein] = CoA + O-heptanoyl-L-seryl-[protein] L-seryl-[protein] + nonanoyl-CoA = CoA + O-nonanoyl-L-seryl-[protein] dodecanoyl-CoA + L-seryl-[protein] = CoA + O-dodecanoyl-L-seryl-[protein] L-seryl-[protein] + tetradecanoyl-CoA = CoA + O-tetradecanoyl-L-seryl-[protein] a fatty acyl-CoA + L-seryl-[protein] = CoA + O-fatty acyl-L-seryl-[protein] Inhibited by 1-[2-cyano-3,12-dioxooleana-1,9(11)- dien-28-oyl]ethylamide (CDDO-EA) with an IC(50) of 60 uM (PubMed:28134508). Inhibited by Fe3+ and Cu2+ and the O-acyltransferase activity is completely blocked over 5 mM Fe3+ and 0.5 mM Cu2+ (PubMed:19501572). Optimum pH is 7.0-7.5. Optimum temperature is 37-50 degrees Celsius. Monomer. Highly expressed in stomach and pancreas (PubMed:18267071). Lower expression in small intestine and colon (PubMed:18267071). Very low expression in testis (PubMed:18267071). Not glycosylated. Mice display a complete lack of octanoylated ghrelin in blood. Belongs to the membrane-bound acyltransferase family.