even purified enzyme preparations are often heterogeneous. for example, preparations of aspartate aminotransferase or cytochrome oxidase can consist of several different forms of the enzyme.  for this reason we consider how different the kinetics of the reactions catalysed by a mixture of forms of an enzyme must be to provide some indication of the characteristics of the species present.  based...

This laboratory has recently reported the isolation of an ethanol-inducible form of rabbit liver microsomal cytochrome P-450, designated isozyme 3a. In view of the reports of others that the hepatotoxicity of acetaminophen is increased in ethanol-treated animals and the human alcoholic, we have determined the activity of the six available P-450 isozymes in the activation of the drug to give an ...

The properties of the microbody malate dehydrogenase (EC 1.1.1.37) (MDH) isozyme from cotyledons of Cucumus sativus L. were compared during development. It is concluded that the isozyme remains unaltered, despite the transition from glyoxysomal to peroxisomal function that occurs during greening of the cotyledons. This conclusion is based on electrophoretic behavior, chromatographic elution fro...

The lactate dehydrogenase (LDH) isozyme patterns of consecutive passages of Chinese hamster embryo cultures were monitored. At early passages the population displayed two LDH bands, M4 and M3H; however, at higher passages the cultures exhibited M2H2, M3H, and M4. When primary cultures of Chinese hamster embryo cells were infected with simian virus 40 (SV4O), no change in the LDH pattern was obs...

Isoelectrofocusing studies of mouse tissue extracts show mice to have a pyruvate kinase isozyme pattern very similar to that of the rat. Moreover, electrofocusing or kinetic assays conducted on liver extracts from normal mice and from mice bearing Ehrlich ascites tumors show that the latter have a higher proportion of the fetal K-isozyme of pyruvate kinase. Serial injection of the supernatant r...

During development of rabbit tissues, characteristic sequential alterations in the LDH isozyme pattern occur, and consist for liver and muscle in loss of the most rapidly migrating anodal bands, and increased activity in the cathodal bands and slower migrating anodal bands. In heart the reverse changes were observed. Comparison of the isozyme patterns observed in various fetal and adult human t...

While acute activation of inhibitory Gi/o-coupled receptors leads to inhibition of adenylyl cyclase, chronic activation of such receptors leads to an increase in cAMP accumulation. This phenomenon, observed in many cell types, has been referred to as adenylyl cyclase superactivation. At this stage, the mechanism leading to adenylyl cyclase superactivation and the nature of the isozyme(s) respon...

To use the equilibrium established by creatine kinase (CK) to determine hepatic free ADP levels, the transcriptional control elements of the transthyretin gene were used to direct expression of the CK B isozyme to the livers of transgenic mice. Activities of CK ranging from 80-250 mumol per min per g (wet weight) were detected in liver extracts from five founder mice. The CK activity was stably...

It has been known that diclofenac is biotransformed into chemically reactive metabolites, which bind covalently to liver microsomal proteins, including cytochrome P450 enzyme(s). We have investigated the ability and selectivity of diclofenac to inactivate P450 enzymes. Preincubation of microsomes of untreated rats with diclofenac in the presence of NADPH resulted in time-dependent loss of testo...