[Comparison of the molecular forms of exonuclease and ribonuclease in normal human spleen]

Molecular forms of exonuclease and ribonuclease from normal human spleen were separated by preparative electrofocusing and characterized by their enzymatic properties. Six molecular forms (E1 to E6) of exonuclease can be separated by isoelectric focusing from human normal spleen. Properties of these molecular forms have been studied: substrate specificity, hydrolysis of paranitrophenyl-thymidine-3'-monophosphate, optimum pH and heat-stability. So two enzymatic groups can be separated: - an acidic group contained forms E2, E3, E4 hydrolysing at high level the paranitrophenyl-thymidine-3'-monophosphate, with optimum pH between 5.0 and 5.5. These three forms were heat labile at 50 degrees C and belong probably to the same isoenzymatic group. - a neutral or more alkaline group was represented by the forms, E1, E5 and E6. These forms hydrolysed at very low level the paranitrophenyl-thymidine-3'-monophosphate and were different by their optimum pH and heat-stability. So, these three forms do not belong to the same isoenzymatic group. Profiles of ribonuclease showed three molecular forms R1, R2 and R3 different from exonucleases by their isoelectric point, optimum pH, substrate specificity and overall heat-stability. These ribonuclease forms differed from one another in optimum pH and probably do not belong to the same isoenzymatic group.