Table 4.

Amino acid concentrations and skeletal muscle BCAT and BCKD activity

	Younger		Older
	UP	HP	UP	HP
Plasma, μmol/l
Total amino acids	2,570±94	2,488±119	2,457±93	2,570±164
Nonessential amino acids	1,575±62	1,544±76	1,592±68	1,640±117
Essential amino acids	995±54	944±53	865±41	930±65
Branched-chain amino acids	415±27	521±42*	390±40	416±23†
Leucine	130±8	134±9	132±7	135±6
KIC	14.4±0.8	16.1±0.6*	13.3±0.7	13.7±0.9†
Lysine	208±8	227±13	253±21	236±16
Skeletal muscle
Lysine concentration, μmol/μg	0.55±0.04	0.81±0.09*	0.74±0.06†	0.72±0.08
Leucine concentration, μmol/μg	0.11±0.01	0.12±0.01	0.12±0.01	0.12±0.01
BCAT activity, nmol·min−1·mg−1	76±9	77±8	107±14	100±16
BCAT protein expression, AU	1.07±0.11	1.17±0.15	1.28±0.20	1.09±0.19
Basal BCKD activity, nmol·min−1·mg−1	147±23	139±20	116±18	123±11
Total BCKD activity, nmol·min−1·mg−1	414±36	368±48	339±39	352±39
%Active BCKD	36±5	37±2	33±2	37±4

Data are means ± SE. BCAT, branched-chain aminotransferase; BCKD, branched-chain α-keto acid dehydrogenase; AU, arbitrary units.

^*P < 0.05 vs. UP;

^†P < 0.05 vs. younger participants (same diet).