Scientists find missing link to understand how plants make vitamin C

April 27, 2007

Hanover, NH--Vitamin C is possibly the most important small molecule whose biosynthetic pathway remained a mystery. That is until now.

A group of Dartmouth and UCLA researchers, who normally work on genes involved in aging and cancer in animals, discovered the last piece of the puzzle, they report in a study published online April 26 in the Journal of Biological Chemistry.

Dr. Steven Clarke of the UCLA Molecular Biology Institute and the Department of Chemistry and Biochemistry explains, "We were working on an interesting gene in worms." One insight led to another until, "We uncovered the last unknown enzyme in the synthesis of vitamin C in plants," said Dr. Charles Brenner of Dartmouth Medical School's Norris Cotton Cancer Center and Department of Genetics.

An essential vitamin for people, vitamin C is well known as an antioxidant and enzyme cofactor. Humans lost the ability to make vitamin C and need to take it up from dietary sources, particularly from plants.

Only in 1998 was a biosynthetic pathway proposed to explain how plants make vitamin C. Research since then has confirmed much of the pathway, although the gene responsible for the seventh step of the proposed 10-step pathway from glucose to vitamin C remained unknown.

The work began in an effort to understand the role of a gene in C. elegans, a tiny worm used as a model for aging studies by researcher Tara Gomez in Clarke's UCLA laboratory. The sequence of the gene suggested that it is related to a family of genes altered in cancer, termed HIT genes, that Brenner studies at Dartmouth.

Collaboration between the two laboratories revealed similarity of the worm gene to the product of the VTC2 gene of Arabidopis thaliana, a small roadside plant whose genetics have been well studied. Mutations in this plant gene had been previously linked to low levels of vitamin C. So the hunt was on to determine how its product would contribute to vitamin C synthesis.

The researchers, led by Brenner and Clarke, reconstituted in test tubes the long mysterious seventh step in vitamin C synthesis, a reaction they describe as the first committed step. They liken the first six steps in vitamin C synthesis to a roadmap with multiple possible routes from glucose to a variety of cellular compounds. Once the product of the sixth step, a compound called GDP-L-galactose, can take the exit marked VTC2, however, the atoms are reconfigured toward making vitamin C, specifically, and little else. The remaining three steps, like a curving driveway, require some turns but no real choices and no backing-up.

Through efforts led by UCLA postdoctoral fellow Dr. Carole Linster, the plant VTC2 enzyme was expressed and purified from bacteria. After preparing their own GDP-L-galactose, the team showed that VTC2 is responsible for the long sought seventh step in vitamin C synthesis.

Since enzymes catalyzing the first committed steps of a pathway represent sites of biological regulation, the researchers hope their discovery may lead to new strategies for increasing vitamin C levels in food crops, which could mean more nutritious foods as well as potentially higher crop yields. They still need to find out what VTC2-related genes do in animals and how these genes may relate to aging and cancer.
Research was funded by grants from the National Institute on Aging and National Institute of General Medical Sciences to Clarke, the National Cancer Institute to Brenner, and a fellowship from the Luxembourg government to Linster. Other members of the research team included UCLA researchers Lital Adler and Brian D. Young and Dartmouth researcher Kathryn Christensen.

For more information, contact: Charles Brenner,, 603-738-1610 (mobile), 603-653-9922 (office); or Steven Clarke,, 310 825-8754 (office), 310 766-1398 (mobile).

The Geisel School of Medicine at Dartmouth

Related Cancer Articles from Brightsurf:

New blood cancer treatment works by selectively interfering with cancer cell signalling
University of Alberta scientists have identified the mechanism of action behind a new type of precision cancer drug for blood cancers that is set for human trials, according to research published in Nature Communications.

UCI researchers uncover cancer cell vulnerabilities; may lead to better cancer therapies
A new University of California, Irvine-led study reveals a protein responsible for genetic changes resulting in a variety of cancers, may also be the key to more effective, targeted cancer therapy.

Breast cancer treatment costs highest among young women with metastic cancer
In a fight for their lives, young women, age 18-44, spend double the amount of older women to survive metastatic breast cancer, according to a large statewide study by the University of North Carolina at Chapel Hill.

Cancer mortality continues steady decline, driven by progress against lung cancer
The cancer death rate declined by 29% from 1991 to 2017, including a 2.2% drop from 2016 to 2017, the largest single-year drop in cancer mortality ever reported.

Stress in cervical cancer patients associated with higher risk of cancer-specific mortality
Psychological stress was associated with a higher risk of cancer-specific mortality in women diagnosed with cervical cancer.

Cancer-sniffing dogs 97% accurate in identifying lung cancer, according to study in JAOA
The next step will be to further fractionate the samples based on chemical and physical properties, presenting them back to the dogs until the specific biomarkers for each cancer are identified.

Moffitt Cancer Center researchers identify one way T cell function may fail in cancer
Moffitt Cancer Center researchers have discovered a mechanism by which one type of immune cell, CD8+ T cells, can become dysfunctional, impeding its ability to seek and kill cancer cells.

More cancer survivors, fewer cancer specialists point to challenge in meeting care needs
An aging population, a growing number of cancer survivors, and a projected shortage of cancer care providers will result in a challenge in delivering the care for cancer survivors in the United States if systemic changes are not made.

New cancer vaccine platform a potential tool for efficacious targeted cancer therapy
Researchers at the University of Helsinki have discovered a solution in the form of a cancer vaccine platform for improving the efficacy of oncolytic viruses used in cancer treatment.

American Cancer Society outlines blueprint for cancer control in the 21st century
The American Cancer Society is outlining its vision for cancer control in the decades ahead in a series of articles that forms the basis of a national cancer control plan.

Read More: Cancer News and Cancer Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to