Gold element silver (as electrum) and also naturally alloyed with copper and palladium. Less commonly, it occurs in minerals as gold compounds, often with tellurium (gold tellurides). Gold is resistant to most acids, though it does dissolve in aqua regia, a mixture of nitric acid and hydrochloric acid, which forms a soluble tetrachloroaurate anion. Gold is insoluble in nitric acid, which dissolves silver and base metals, a property that has long been used to refine gold and to confirm the presence of gold in metallic objects, giving rise to the term "acid test". Gold also dissolves in alkaline solutions of cyanide,
Methylmalonic acid Methylmalonic acid Methylmalonic acid (MMA) (conjugate base methylmalonate) is a dicarboxylic acid that is a "C"-methylated derivative of malonate. The coenzyme A linked form of methylmalonic acid, methylmalonyl-CoA, is converted into succinyl-CoA by methylmalonyl-CoA mutase, in a reaction that requires vitamin B as a cofactor. In this way, it enters the Krebs cycle, and is thus part of one of the anaplerotic reactions. Increased methylmalonic acid levels may indicate a vitamin B deficiency. However, it is sensitive (those with the disease almost always test positive) but not specific (those that do not have the disease do not always test negative).