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KMID : 0377619670130060523
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Korean Jungang Medical Journal
1967 Volume.13 No. 6 p.523 ~ p.537
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partial Purification and Isozymic Nature L-Aspartate
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Kang Sung-Yong
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Abstract
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In the multidisciplinary study of metabolic regulatory and control mechanisms in higher organisms much of the emphasis is now put on the fine details of enzyme structure, synthesis, and action. This is quite a logical tendency, since it is not possible to understand fully the control of an enzyme activity if one does not also fully, understand its structure. One of the outstanding examples of the way study of enzyme structure itself may in turn lend insight into the enzyme´s regulation is the discovery that many enzymes are heterogenous. The enzyme may exist in several physical forms, called isozymes (I), composed of different polypeptide chains, each species being enzymatically active.
The probable significance of the lactate dehydrogenase isozyme system, for example, has come to light over the past several years. As seen. in a starch gel after electrophoresis and staining, the isozyme bands are arbitrarily numbered one through five, from the anodal to the cathodal ends of the gel. The five isozymes are produced by random, tetrameric association of two different polypeptide subiunits which are under separate genetic control (2-5). Two polypeptides have been designaaed by Markert (6) as the B and A subunits, and thee composition of the five, isozyme is denoted, from. lactate dehydrogease 1 through 5 respectviely as B4, B3A2, B2A2, and A4. Thus, the first and fifth bands are homogenous tetramer, while the three intermediate bands are heterogenous, or the so-called `hybrid´ forms.
At this time, therefore, it is fair to. state that the findings of different lactic dehydrogenase isozyme patterns together with other numerable patterns obtained from various enzymes in different tissues, and of shifts of the patterns during development, during certain disease states, and in response to various nutritional reaction may underlie the divers physiological responses elicited by the glucocorticosteriods. However, an initial physiological response to treatment with glucocorticosteriods may involved a rapid increase in the availability of glucose which result in measurable glycogen deposition within several hours. A secondary response, therefore, to prolonged cortisone administration or stress results in utilization of tissue protein that can progress to a state of negative nitrogen. balance.
This rise in the activity due o cortisone treatment seems to be a reflection of ;the increased activity in the anodal fractions in the present work especially the isozyme VI, though there was a fall observed in the V isozyme. The anodal isozymes as compared to the cathodal isozymes, seems to change their pattern of isozyme distribution (Table III) significantly. Therefore, cortisone seems enhance the supernatant aspartate fraction more than the mitochondrial fraction, which awaits, however, further investigations. Unlike the alanine transaminase reported by Gatehouse et al. (48) , who shoved no physical differences between the enzyme preparations from normal and glucocorticoid treated animals, the present preparation of the aspartate transaminase seems to alter their anodal distribution pattern as mentioned above.
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