The microbiological determination of carnosine and its formation by rat liver slices.

Microbiological methods have been applied previously to the determination of carnosine and anserine. Mueller (1) demonstrated that the diphtheria bacillus was able to split L-carnosine enzymatically and use the liberated @alanine for growth. Apparently a specific enzyme was involved, as the organism did not cleave the D isomer. It was not determined whether anserine might also be utilized by the diphtheria bacillus for growth. Fuller, Neuberger, and Webster (2) employed Saccharomyces cerevisiae to estimate the p-alanine content of hydrolyzed protein-free muscle extracts. On the basis of this value they estimated the amount of carnosine plus anserine present in the tissue. In the present study, the determination of carnosine is based on the microbiological assay of histidine in deproteinized muscle extracts both before and after acid hydrolysis. Leuconostoc mesenteroides P-60 was the assay organism used. The chief advantages derived from this method are its applicability to very small amounts of tissue with the retention of a high degree of accuracy, plus the fact that carnosine may be estimated in the presence of histidine or other imidazoles which normally react with the diazo reagent in the widely used calorimetric procedure of Koessler and Hanke (3). With the availability of an accurate method for the determination of carnosine in the presence of histidine or @alanine, it was possible to study the formation of carnosine by rat liver slices in the presence of these amino acids. This process is of interest from two standpoints: first as a way to observe whether liver is a potential source of carnosine, for very little is known of the origin of this compound, and second as a model for studying the synthesis in vitro of a peptidic bond.