Abstract: A urease-free creatinine iminohydrolase enzyme preparation obtained from an aerobic soil microorganism. The enzyme of the preparation preferably has a molecular weight of from about 250,000 to 300,000; a maximum activity at a pH between 7 and 8 as measured at 37.degree. C.; a K.sub.m of about 3 to 5 mM for creatinine as measured at 37.degree. C., pH 7.5; and a specific activity for creatinine of at least about 1.0 unit per milligram of protein in the preparation as measured at 37.degree. C., pH 7.5. The preferred enzyme preparation is derived from the aerobic soil microorganism ATCC 31,546. Assay methods, compositions, and elements containing the aforementioned urease-free creatinine iminohydrolase for the determination of creatinine in an aqueous liquid are also disclosed.

Abstract: A fermentation process and improved aqueous nutrient medium is used for the production of urease-free creatinine iminohydrolase from an aerobic soil microorganism. In the process, a fresh sample of the microorganism grown on a creatinine-containing maintenance medium is transferred to a microbial growth medium to grow the microorganism, the growing microorganism is then transferred to a production medium to produce microorganism in which creatinine iminohydrolase production has been induced, and the desired enzyme is then extracted from the microorganism. An improved aqueous nutrient medium for use as the aforementioned production medium is disclosed.

Abstract: A process for the recovery of an intracellular enzyme from an aerobic soil microorganism is disclosed. The recovery method is carried out by(a) forming an aqueous suspension of microbial cells containing the desired intracellular enzyme,(b) disrupting the microbial cells in the suspension to release the enzyme from the cells, and(c) before, during, or after step (b) and prior to removal of disrupted microbial cells and other cellular components, introducing a water-miscible organic solvent into the suspension to form a mixture of the organic solvent and the enzyme-containing suspension.The desired enzyme is retained in the liquid phase of the mixture formed in step (c) while undesired cellular components such as other microbial cell proteins precipitate therefrom.