Studies showing that addition of cysteine, glutamate, or glycine does not enhance glutathione synthesis also support the role of GCL as a metabolic control point in the pathway (Meyer and Fricker, 2002)
doi:10.1089/ars.2007.1957, PMID: 18522489 Sheehan D, Meade G, Foley VM, Dowd CA (2001) Structure, function and evolution of glutathione transferases: implications for classification of non-mammalian members of an ancient enzyme superfamily
There are also methylmalonic acid (MMA) tests that provide a more complete analysis of the vitamin B12 available in your body
Lower tolerance of sulfur-containing foods such as garlic, onion, and leek may be reversed by supplementation with molybdenum and/or vitamin B12, often deficient in affected individuals

Water(Aqua), Glycerin, Acrylates Copolymer, **Niacinamide, Carrageenan, Butylene Glycol, 1,2-Hexanediol, Glucomannan, Hydroxyacetophenone, Cellulose Gum, Calcium Chloride, Ceratonia Siliqua (Carob) Gum, Allantoin, Gardenia Florida Fruit Extract, Polyglyceryl-10 Laurate, Potassium Chloride, Propanediol, Cyamopsis Tetragonoloba (Guar) Gum, Sucrose, Dipotassium Glycyrrhizate, Dextrin, Adenosine, Caprylyl Glycol, Arginine, Ethylhexylglycerin, Panthenol, Sodium Phytate, Sphingomonas Ferment Extract, **Glutathione, Phosphatidylcholine, Squalane, Acetyl Glucosamine, **Arbutin, **Alpha-Arbutin, **Ascorbic Acid, **Kojic Acid, Centella Asiatica Extract, Citrus Limon (Lemon) Fruit Extract, Sodium Hyaluronate, Hydroxypropyltrimonium Hyaluronate, Tocopheryl Acetate, Sodium Acetylated Hyaluronate, Hydrolyzed Hyaluronic Acid, Hyaluronic Acid, Sodium Hyaluronate Crosspolymer, Hydrolyzed Sodium Hyaluronate, Potassium Hyaluronate