[Changes in enzyme activities in early passages of cultured fibroblasts].

The specific activities and variability coefficients (Wn) of specific activities of seven enzymes (5 lines) of cultured embryonic human fibroblasts were studied. The experiments were carried out on the 2nd--6th passage (between 12th and 19th passages); in each passage simultaneously up to 3-10 vials collected on the 8th cultivation day were analyzed. According to the Wn value, the enzymes under study can be divided into two groups, i.

[Detection of phenylalanine hydroxylase activity in human leukocytes and fibroblasts].

The data obtained indicate the presence of phenylalanine hydroxylase activity in human leucocytes and fibroblasts. The following methods were used: estimation of accumulation of the oxidized form of the pteridine cofactor after Ayling and coworkers and radiochemical method. Probably this activity is connected with cell membranes and can be solubilized by treatment of cells by Tritone X-100.

Estimation of correlation of lactate dehydrogenase subunits mole quota based on differences in substrate inhibition.

A kinetic method of estimating the mole quota ratios of the human lactate dehydrogenase (LDH) H and M subunits based on differences in substrate inhibition of LDH isoenzymes by lactate is porposed. Stability of kinetic constants for a prolonged period of time is demonstrated. The dependence of the activity ratios on the contribution of the mole quota of the M-subunit of LDH is studied under conditions of low and high substrate concentrations.

[Isoenzyme system of lactate dehydrogenase in human cells and tissues].

Comparative investigation of total activity and molar ratio of M-polypeptide chains (MM) of lactate dehydrogenase in diploid human cells with normal karyotype is carried out. It is found that the activity values in the passages studied (from 8 to 22) varies considerably, the variation coefficient Wn being 47.5%.

[Use of differences in substrate inhibition for determination of the interrelationship between molar fractions of lactate dehydrogenase subunits].

A kinetic method of estimating the ratio of mole quota of H and M human lactate dehydrogenase (LDG) subunits is proposed, based on changes in substrate inhibition of LDG isoenzymes with lactate. Stability of kinetic constants for a long period of time is demonstrated. The dependency of activities ratio under low and high substrate concentration on the contribution of mole quota of LDG M subunits is studied.