Lipid Metabolism Has Been Good to Me George M
Total Page：16
File Type：pdf, Size：1020Kb
REFLECTIONS Lipid metabolism has been good to me https://doi.org/10.1016/j.jbc.2021.100786 George M. Carman* From the Department of Food Science and the Rutgers Center for Lipid Research, New Jersey Institute for Food, Nutrition, and Health, Rutgers University, New Brunswick, New Jersey, USA Edited by the Reflections and Classics Committee headed by Patrick Sung My career in research has flourished through hard work, program director of the National Science Foundation), supportive mentors, and outstanding mentees and collabora- encouraged me to pursue a research career in biochemistry; tors. The Carman laboratory has contributed to the under- she continues to be a mentor and friend. My MS degree standing of lipid metabolism through the isolation and advisor, John Keller, introduced me to laboratory research characterization of key lipid biosynthetic enzymes as well as and gave me an appreciation for science in a broader context through the identification of the enzyme-encoding genes. Our by encouraging me to attend meetings of the Theobald Smith findings from yeast have proven to be invaluable to understand Society for Microbiology (local branch of the American So- regulatory mechanisms of human lipid metabolism. Several ciety for Microbiology). He also encouraged me to apply to rewarding aspects of my career have been my service to the the University of Massachusetts (PhD, 1977) where Robert Journal of Biological Chemistry as an editorial board member Levin had an open graduate research position in food and Associate Editor, the National Institutes of Health as a microbiology. I did not realize that my PhD degree would be member of study sections, and national and international sci- in Food Science or that I would have to take undergraduate entific meetings as an organizer. I advise early career scientists and graduate courses in the subject to pass the qualifying to not assume anything, acknowledge others’ accomplishments, examination. It was during my doctoral research that I first and pay it forward. learned how to purify and characterize an enzyme. I worked on a pyridoxal-5-phosphate-dependent enzyme named tyro- sine phenol-lyase, an enzyme from the bacterium Aeromonas Reflections articles, which were introduced to commemo- phenologenes that produces the toxin phenol in fish (1). There rate the Journal of Biological Chemistry (JBC) Centenary in are three products of this reaction, namely phenol (identified 2005, highlight the careers of scientists who have made the by gas chromatography), pyruvate (identified by 2, 4- journal a home for their work. Until now, I have authored 105 dinitrophenylhydrazine derivatization), and ammonia (identi- papers in the JBC. I am truly honored that Herbert Tabor, a fied by nesslerization); Levin had me confirm the stoichio- long-time editor-in-chief (EIC) of the journal, invited me to metric formation of each of the products. A routine assay write my story. measured the formation of pyruvate from tyrosine by following a decrease in A340 nm in the presence of lactate Education and how I wound up at Rutgers University dehydrogenase and NADH (1). Under Levin’s tutelage, I had I grew up in humble surroundings in Jersey City, New Jer- to improvise for basic biochemical equipment; for example, sey. My mother was the only one in the family who finished we made chromatography columns out of glass pipes and high school prior to my older sister, and I was the first in my used makeshift PAGE units and casting tubes. He also made family to attend college. I always did well in biology and the laboratory recycle all solvents. This training in frugality chemistry classes, and so, I gravitated to those subjects. I went was very helpful when I started my own laboratory without to William Paterson College (BA, 1972) where I was recruited enough funds for supplies and equipment. by a swimming coach Arthur Raidy; I swam breast stroke and Levin had done a sabbatical at Baylor College of Medicine the individual medley for the college team. I majored in and glorified Houston as a hotbed for basic research. So, when biology and minored in chemistry. John Rosengren (biology it came time to seek a postdoctoral position, I applied to teacher) and Ashot Merijanian (chemistry teacher) were biochemistry laboratories in Houston. One laboratory that I † particularly encouraging; I wanted to be a college professor applied to was that of Bill Dowhan (2) at the University of like them, and so, I sought an advanced degree. Texas Medical School. Bill’s laboratory was studying the I pursued an MS degree (1974) in biology at Seton Hall structure and function of Escherichia coli membranes with an University where I served as a teaching assistant in biology emphasis on the genes and enzymes responsible for synthe- and conducted a research project on the expression of sizing phospholipids. Just a few years earlier, Singer and mannitol dehydrogenase activity in Agrobacterium. A mem- Nicholson published the famous fluid mosaic model mem- ber of my thesis committee, Elvira Doman (now a retired brane structure (3), and understanding the regulation of * For correspondence: George M. Carman, [email protected]. † Reflections article. J. Biol. Chem. (2021) 297(1) 100786 1 © 2021 THE AUTHOR. Published by Elsevier Inc on behalf of American Society for Biochemistry and Molecular Biology. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). REFLECTIONS: Lipid metabolism has been good to me membrane phospholipid synthesis was becoming an area of After my first year in Bill’s laboratory, I began to look for a interest that I wanted to be involved in. I received an offer permanent position because I was worried about my ability to from Bill by phone, accepted it, and headed for Houston find a faculty position. I applied for positions in numerous during the first week of January 1977. He later told me that the biochemistry departments but did not receive a positive reason he had accepted me into his laboratory was because I response. However, I was offered two positions, one at General had studied a yellow-colored pyridoxal-5-phosphate-depen- Mills in Minneapolis and the other in the Department of Food dent enzyme and he had also studied a similar enzyme, D- Science at Rutgers University because of my degree in food serine dehydratase (4). Whereas I thought I would be purifying science. I was first drawn to General Mills because of a much enzymes involved in phospholipid metabolism, I spent half of higher salary and the living environment in Minneapolis, but I my time chemically synthesizing the liponucleotide CDP– was being hired to work on Betty Crocker Potatoes Au Gratin, diacylglycerol (DAG) and its fatty-acyl analogs for substrate- and this project was not enticing. A faculty position was my specificity studies of the CDP–DAG–dependent enzyme real goal, but I wanted a position in biochemistry, not one in phosphatidylserine (PS) synthase (5). I learned a great deal food science. Bill was surprised to learn that I would be leaving about organic synthesis and became an expert in rotary his laboratory after such a short time, but he recommended evaporation. The enzyme kinetic experiments were based on a that I take a position at Rutgers; he reasoned that it was my † “surface dilution kinetics” model that Ed Dennis (6) and best option for a faculty position given my doctoral degree in colleagues devised for interfacial enzymes (7, 8). To perform food science. I accepted the offer from Rutgers because I was the kinetic studies, I developed a continuous spectrophoto- being hired for my biochemical expertise and could do any metric assay whereby the release of CMP from CDP–DAG is research in the broad area of food science. An extenuating coupled to the oxidation of NADH in the presence of CMP circumstance was that my mother had just been diagnosed kinase, pyruvate kinase, and lactate dehydrogenase (9). Of with pancreatic cancer and I wanted to be near home in New course, I was familiar with coupled spectrophotometric assays Jersey. So, after 1.5 years, I left Houston in June 1978 to using lactate dehydrogenase from my doctoral studies. Previ- embark on my independent research career. ously, a cumbersome radioactive assay was used to measure PS synthase activity by monitoring the incorporation of water- The research that shaped my career soluble radiolabeled serine into chloroform-soluble radio- My startup package at Rutgers included $10,000 for labeled PS (10). equipment, which I used to purchase a Gilford spectropho- For the newly developed spectrophotometric assay, I had to tometer, $7000 for supplies, and a graduate student assistant. purify the CMP kinase, which was not commercially available. The supply money was tied to an existing United States During this process, I learned many tricks from Bill that I did Department of Agriculture–New Jersey Agricultural Experi- not know from my doctoral research on tyrosine phenol-lyase. ment Station project from the professor I replaced, meaning Bill had much experience in purifying enzymes (4, 10–14), and that I would be required to investigate the postharvest physi- in fact, he purified the first membrane-associated enzyme, the ology of potatoes and tomatoes. I therefore set off to identify E. coli PS decarboxylase (15). My postdoctoral work merged membrane-associated phospholipid biosynthetic enzymes in my interests in enzymology and chemistry, which laid a these foods. I focused on phosphatidylinositol (PI) synthase foundation for much of the biochemical research in my career. because of my familiarity with PS synthase; both enzymes One important thing that I learned from Bill was how to listen utilize CDP–DAG as a substrate (21, 22)(Fig. 1). Moreover, to laboratory members and let them know that their ideas and the spectrophotometric assay I had developed for CDP–DAG– opinions were important.