Comparative studies of liver and muscle aldolase. I. Effect of carboxypeptidase on catalytic activity.
نویسندگان
چکیده
The demonstration (l-3) of a distinctive pathway of fructose metabolism in liver via the aldol cleavage of fructose l-phosphate emphasized the possibilty in this tissue of an enriched catalytic system for the facilitation of this reaction since the classical fructose-l ,gdiphosphate aldolase isolated from muscle tissue exhibits relatively little activity toward fructose l-phosphate. The early evidence of Leuthardt et al. (4) suggested the presence in liver of two aldolases, one acting primarily on fructose 1,6diphosphate (and presumably identical with the muscle enzyme), the other, a new enzyme, facilitating the aldol cleavage of fructose l-phosphate. However, Peanaskyand Lardy (5) isolated the liver enzyme in crystalline form and showed that the relative activity toward fructose l-phosphate was much higher than the muscle enzyme. The fructose 1,6-diphosphate to fructose lphosphate activity ratio of the crystalline liver enzyme did not change during the purification procedure. These studies suggested that the aldolases from liver and muscle could be distinguished clearly on the basis of substrate specificity. In spite of this fact, there is an intriguing resemblance in the molecular properties of the bovine liver and rabbit muscle aldolases: the number of sulfhydryl groups per g of protein (5-7) ; the molecular weights as determined by sedimentation and diffusion measurements (5, 8); and the electrophoretic mobilities (5, 9) of the two enzymes are similar, perhaps within the error of the measurements. Recently, Drechsler, Boyer, and Kowalsky (10) have reported that removal of three carboxyterminal tyrosine residues from muscle aldolase by carboxypeptidase markedly decreases the fructose 1,6-diphosphate cleavage activity, without loss of fructose l-phosphate cleavage activity. The resulting carboxypeptidase degraded aldolase has a fructose 1,6-diphosphate to fructose l-phosphate activity ratio which is not far removed from that of liver aldolase. These observations have suggested the possibility that muscle and liver aldolase may have strong elements of structural and catalytic similarity. Accordingly, a comparative study of these enzymes has been initiated. In the present paper, the effect of carboxypeptidase on the aldol cleavage and the hydrogen exchange activities, as well as the specificities of liver and muscle aldolase will be described.
منابع مشابه
Comparative Studies of Liver and Muscle Aldolase. Ii. Immunochemical and Chromatographic Differentiation.
Crystalline fructose diphosphate aldolase preparations obtained from rabbit muscle and bovine liver differ in catalytic efficiency (fructose diphosphate cleavage activity of muscle aldolase is about 10 times that of the liver enzyme) and substrate specificity (the fructose diphosphate to fructose l-phosphate activity ratio is 50 for muscle and 1 for liver aldolase) (2). In spite of these distin...
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ورودعنوان ژورنال:
- The Journal of biological chemistry
دوره 236 شماره
صفحات -
تاریخ انتشار 1961