The invention relates to pharmaceutical compositions for use in the therapy of pathological states related to disturbances of the nervous stimulus in the central (CNS) and peripheral (PNS) nervous system containing as an active substance the cytidine monophosphate of 5-acetamido-3,5-dideoxy-D-glycero-D-galactononulosaminic acid. Moreover the invention relates to an improved method for preparing said compound by the condensation of cytidine triphosphate (CTP) with N-acetylneuraminic acid (NANA), catalyzed by the enzyme CMP-transferase (CMP-acylneuraminate synthase) (EC 2.7.7.43).

A stable intermediate composition of human or animal serum or a protein solution which contains a stable component consisting essentially of a mixed disulfide or dithiosulfonate derived from creatine kinase (ATP: creatine N-phosphotransferase, EC 2.7.3.2) is disclosed as well as its employment as a reference standard for the assay of creatine kinase.

A lyophilized product containing monothioglycerol, sulfhydryl-requiring enzyme and a specially prepared serum matrix, useful in the clinical laboratory when reconstituted, is provided.

A stable human serum based control for the assay of Total LD and CK and their isoenzymes. This control may be lyophilized and reconstituted and still provide the same enzyme activity prior to lyophilization, for seven (7) days after reconstitution, if stored in the dark at or about 2.degree.0 to 8.degree. C. No thiol compounds other than the amount normally used to purify CK isoenzymes are found in this highly stable control.

A reagent for the determination of creatine kinase is comprised of a reagent group containing N-acetylcysteine and ethylenediaminetetraacetic acid and a reagent group containing magnesium, whereby the stability thereof is acheived.