Summary
Prochymosin variants were analysed in single abomasa from 67 foetuses (3–9 months of gestation) and 33 calves (about 6 weeks old) of Black‐and‐White cattle collected in a slaughter house. The method of agarose gel electrophoresis followed by detection of proteolytic activity was used. Three distinct prochymosins A, B and C that occurred singly or in pairs (with equal proteolytic activities of both components) were found. Chymosin A, B and C obtained after conversion of corresponding prochymosins, demonstrated similar electrophoretical mobilities like the three chymosin fractions contained in commercial rennin (Sigma, USA). Our chymosin B showed identical mobility as the amidated form of recombined chymosin B contained in Chymogen (Chr. Hansen's Lab., Danmark A/S).
Prochymosin A, B and C in the examined animals were precursors of corresponding chymosins and were controlled by three separate codominant alleles.
The following prochymosin phenotypes were found: AA (30), AB (32), AC (4), BB (29), BC (4) and CC (1). Chi‐square analysis demonstrated significant differences between the observed and expected numbers of phenotypes. The gene frequencies of prochymosin A, B and C were 0.48, 0.47 and 0.05, respectively.