Abstract: In a process for the determination of total or bound cholesterol by liberating any bound cholesterol using cholesterol esterase and simultaneously or subsequently determining the liberated cholesterol and any initially free cholesterol with a cholesterol reacting enzyme, the improvement comprising using as the cholesterol reacting enzyme an NAD or NADP-dependent cholesterol dehydrogenase obtained from an anaerobic microorganism, e.g., Eubacterium sp. ATCC 21408, or from mammalian tissue, e.g., liver.

Abstract: In a process for the determination of substrates or enzyme activities in a test batch, utilizing a conventional redox reaction as a measurement reaction, the improvement comprising carrying out the process in the presence of ascorbate oxidase; the addition of ascorbate oxidase substantially eliminates the interfering effect of ascorbic acid frequently found in the test sample.

Abstract: Cholesterol oxidase free of unstabilizing residual traces of detergent is activated by adding to the cholesterol oxidase, before use thereof, at least one surface-active compound with lipophilic and hydrophilic properties. Diagnostic agents for determining cholesterol comprising cholesterol oxidase, a hydrogen peroxide detection system, a buffer, and at least one surface-active compound having lipophilic and hydrophilic properties are provided.

Abstract: A new enzyme, cholesteroloxidase, is prepared by recovering same from microorganisms, preferably by washing a cholesterol-converting microorganism with butanol/water, disintegrating the microorganism culture and extracting same with a buffer solution containing a non-ionic surface-active agent, and isolating cholesterol oxidase from the extract.

Abstract: Cholesterol oxidase which oxidizes cholesterol with oxygen to give cholestenone and hydrogen peroxide, is prepared by culturing Nocardia erthropolis ATCC 17895, Nocardia erthropolis ATCC 4277, Nocardia formica ATCC 14811 or Proactinomyce erythropolis NCIB 9158 first on a peptone-containing mineral salt medium and thereafter on at least one sterol compound as the sole source of carbon, and then isolating the cholesterol oxidase formed from the cultured micro-organism, wherein said sterol compound is of the formula ##STR1## in which R.sub.1 and R.sub.2 are hydrogen or together represent a double bond,R.sub.3 and R.sub.4 are hydrogen or together represent a double bond, andR.sub.5 is hydrogen or alkyl containing up to 3 carbon atoms.

Abstract: The new enzyme steroid-.DELTA.-isomerase is provided, as well as a process for producing same, comprising digesting a micro-organism containing said isomerase, extracting same by destruction of the cell wall with a buffer solution containing a non-ionic surfactant, centrifuging the resulting mass and discarding the precipitate, applying the extract to an anion exchanger, eluting the enzyme with a buffer solution containing a non-ionic surfactant, heating the eluate, separating the precipitate and isolating the enzyme therefrom from the supernatant.