Enzyme Crystals (IMAGE) Max Planck Institute for Marine Microbiology Caption Pictures of F420H2-oxidase crystals obtained aerobically with a typical size of 0.1 mm. With oxygen the Fe and flavin inside the enzyme give the natural yellow color to the crystals. Credit Max Planck Institute for Marine Microbiology/T. Wagner Usage Restrictions Only to be used in the context of this publication and citing the correct copyright License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.