Enzyme Secretion and the Incorporation of P32 into Phospholipides of Pancreas Slices (Hokin, M. R., and Hokin, L. E. (1953) J. Biol. Chem. 203, 967–977) Phosphoinositides and Protein Secretion in Pancreas Slices (Hokin, L. E., and Hokin, M. R. (1958) J. Biol. Chem. 233, 805–810) Mabel R. Hokin (born Mabel Neaverson) and Lowell E. Hokin met in Hans Kreb's department at the University of Sheffield and married soon after. During their time in Sheffield, the Hokins started investigating what they thought was an increase in the incorporation of 32P into RNA caused by the acetylcholine-induced stimulation of pancreatic slices. However, before they could purify the RNA, they moved to McGill University in Montréal, Québec, and brought their radiolabeled samples with them. Once established in Montréal, they continued with their experiments but noticed that as they purified the RNA the radioactivity was lost. Investigating this phenomenon further, they found that most of the radioactivity was incorporated into the phospholipid fraction. This was a surprising discovery as up until then phospholipids were regarded as inert structural components of membranes. The Hokins' studies on 32P uptake into phospholipids during enzyme secretion in pancreas slices are published in the first Journal of Biological Chemistry (JBC) Classic reprinted here. The Hokins incubated pigeon pancreas slices with various compounds along with 32P to see the effects on phosphate incorporation into phospholipids. They found that when enzyme secretion was stimulated by acetylcholine or carbamylcholine, both of which induce amylase secretion, the incorporation of 32P into phospholipids was on average 7.0 times greater than in control tissue. Separating individual phospholipids for analysis was difficult at that time, but fortunately Rex Dawson devised a method that permitted the analysis of diacylglycerophospholipids by deacylation and two-dimensional separation of the water-soluble backbone (1Dawson R.M.C. The measurement of 32P labeling of individual kephalins and lecithin in a small sample of tissue.Biochim. Biophys. Acta. 1954; 14: 374-375Crossref PubMed Scopus (58) Google Scholar). The Hokins used this method to show that hormone stimulation of pancreatic slices mainly increased the rate of 32P incorporation into phosphoinositide but that phosphatidylcholine, phosphatidylserine, and phosphatidic acid also contained radiolabeled phosphate (2Hokin L.E. Hokin M.R. Effects of acetylcholine on the turnover of phosphoryl units in individual phospholipids of pancreas slices and brain cortex slices.Biochim. Biophys. Acta. 1955; 18: 102-110Crossref PubMed Scopus (161) Google Scholar). This was the first demonstration of receptor-stimulated lipid turnover, and it later became known as the “PI effect.” The second JBC Classic reprinted here presents the details of the Hokins' study of phosphoinositide metabolism in relation to protein secretion in the pancreas. They incubated pigeon pancreas slices with either NaH2P32O4, [2-3H]inositol, or [1-14C]glycerol and extracted the lipids from the tissue and separated them by paper chromatography. They were able to identify seven phospholipids containing 32P as well as two radioactive monophosphoinositides. From these data they concluded, “the present work indicates that phosphoinositides are involved in the secretion of protein from the inside of the pancreatic acinar cell into the lumen... It is tempting to think that the active transport out of the cell of many other types of molecules may involve phosphoinositides.” In 1957 the Hokins moved to Madison, Wisconsin, where they both joined the faculty of the University of Wisconsin-Madison Medical School. There they showed that other tissues exhibit similar responses when provoked to secrete. In 1964 the Hokins suggested that phospholipase C-catalyzed phosphatidylinositol hydrolysis might initiate the PI effect. Later it was confirmed that the initiating event was the phospholipase C-catalyzed hydrolysis of phosphatidylinositol 4,5-bisphosphate and that 3-kinase-catalyzed formation of phosphatidylinositol 3,4,5-triphosphate was a second widespread signaling reaction. The Hokins' initial work on stimulated phosphoinositide turnover in secretory tissues motivated a large number of other investigators to focus their research on the PI effect and second messengers. Eventually they would discover that the Hokins' inositol phospholipids play important roles in transmembrane signaling and many other cell regulatory processes. 1All biographical information on Mabel R. Hokin and Lowell E. Hokin was taken from Refs. 3Michell B. Obituary: Mabel R. Hokin (1924–2003).The Biochemist. 2003; (December)Crossref Google Scholar and 4Irvine R.F. 20 years of Ins(1,4,5)P3, and 40 years before.Nat. Rev. Mol. Cell. Biol. 2003; 4: 586-590Crossref PubMed Scopus (72) Google Scholar. 1All biographical information on Mabel R. Hokin and Lowell E. Hokin was taken from Refs. 3Michell B. Obituary: Mabel R. Hokin (1924–2003).The Biochemist. 2003; (December)Crossref Google Scholar and 4Irvine R.F. 20 years of Ins(1,4,5)P3, and 40 years before.Nat. Rev. Mol. Cell. Biol. 2003; 4: 586-590Crossref PubMed Scopus (72) Google Scholar.