text: In humans, the glycerol phosphate shuttle is primarily found in brown adipose tissue, as the conversion is less efficient, thus generating heat, which is one of the main purposes of brown fat. It is primarily found in babies, though it is present in small amounts in adults around the kidneys and on the back of our necks. The malate-aspartate shuttle is found in much of the rest of the body.
  The shuttles contains a system of mechanisms used to transport metabolites that lack a protein transporter in the membrane, such as oxaloacetate.