TISSUE-SPECIFIC ACTIVITY OF PENTOSE CYCLE OXIDATIVE-ENZYMES DURING FEEDER LAMB DEVELOPMENT

Relationships between pentose cycle oxidative activity and differentia l fat growth were evaluated. Rambouillet wether lambs (n = 60) were sl aughtered serially at 0, 40, 80, and 120 d on feed (15 lambs/group). R ack dissection and kidney fat weights were collected, and longissimus muscle i.m. fat content was determined. Postmortem longissimus muscle, s.c. fat, intermuscular fat (INT), and kidney fat (KP) samples were a ssayed in vitro for glucose-6-phosphate dehydrogenase (G6PDH) and 6-ph osphogluconate dehydrogenase (6PGDH) activity (nanomoles-minute-1. gra m of tissue-1), and samples were subjected to electrophoresis (PAGE) t o separate tissue-specific isoforms. Allometric coefficients for rack components indicated that s.c. fat was the earliest-maturing, slowest- growing depot, INT was the latest-maturing, fastest-growing depot, and i.m. fat was intermediate (P < .05). Kidney fat grew faster than carc ass weight and, as carcass weight increased, the growth rate of KP acc elerated (P < .05). Enzyme activities increased until 40 d on feed and declined thereafter. Activities differed across tissues and time on f eed end points (P < .05). Ratios of G6PDH:6PGDH, reflecting flux throu gh the oxidative phase of the pentose cycle and, therefore, lipogenic activity, suggested growth patterns similar to those indicated by allo metric analysis, except in the i.m. fat depot. Development of i.m. fat initially was intermediate to KP and INT, but G6PDH:6PGDH ratios incr eased with time on feed, suggesting a different regulatory mechanism a nd maturing pattern. Multiple forms of G6PDH were detected with PAGE, and although polymorphism was not detected, a tissue-specific isoform was isolated for INT fat.